A day after President Nayib Bukele of El Salvador offered to imprison convicted criminals from the United States, including U.S. citizens, the question of whether such a plan could actually be accepted and implemented was still unanswered.

Secretary of State Marco Rubio, who stopped in El Salvador while visiting Central America this week, said on Tuesday that the Trump administration would have to “study” the offer from Mr. Bukele to jail convicts from the United States, for a fee. “But it’s a very generous offer,” he said.

Mr. Rubio himself said it was unclear if the United States could legally send convicts, including Americans, to a foreign prison.

But the proposal has drawn attention to the prisons that Mr. Bukele has used in recent years to cripple the gangs that once ran rampant in El Salvador. They have become symbols of his strength and popularity, including with Mr. Trump — even as human rights groups say the crowded prisons are holding pens for tens of thousands of people rounded up in arrests that have ensnared innocents.

Analysts say it is unlikely such a plan would hold up in court, particularly where it concerns U.S. citizens.

But whether or not Mr. Bukele’s offer is ever actually acted on, analysts said it serves as a way for both nations’ governments to project a shared vision of a tough approach to lawbreakers.

“The announcement is a P.R. win,” said Gustavo Flores-Macías, a professor of government and public policy at Cornell University who specializes in Latin America. It allows Mr. Bukele to show he is all-in for Mr. Trump, and bolsters the Trump administration, “which is looking to dissuade undocumented migration by raising the stakes if apprehended.”

And yet, whatever its chances of being out into practice, Mr. Bukele’s announcement immediately sparked concern among human rights groups in the United States and beyond, which warned that the Bukele administration’s anti-gang crusade has come at the expense of human rights.

“While the gangs no longer constitute a threat, a system of terror and repression has emerged in the country,” said Ana María Méndez Dardón, the Central America director at the Washington Office for Latin America, a nonprofit human rights group.

At a hearing before the Inter-American Commission on Human Rights in July 2024, Alexandra Hill Tinoco, El Salvador’s foreign minister, said the country is “meeting all international standards” for prisoners and added that reports of human rights violations are “baseless accusations and far from our reality.”

What has Bukele’s approach to crime looked like?

El Salvador was once known as the hemisphere’s murder capital — with one of the highest homicide rates anywhere in the world.

But in 2022, Mr. Bukele declared a state of emergency to quell gang violence, and sent the military into the streets, arresting tens of thousands of people around the country, accusing them of gang ties or other crimes. More than 25,000 were imprisoned in the first weeks of Mr. Bukele’s crackdown.

Nearly three years later, the state of emergency has yet to be lifted.

In that time, the nation has undergone a remarkable transformation. Homicides have sharply decreased, and extortion payments that gangs demanded from businesses and residents also declined.

As a reminder of the government’s zero tolerance, tough-on-crime policies, photos and videos are often circulated that show scores of inmates, sometimes shirtless and clad only in boxers, bending over with their hands on their shaven heads.

Mr. Bukele earned adulation from leaders in the region and beyond, and most Salvadorans support him, not in spite of his strongman tactics but because of them.

In November, his approval rating was 91 percent, according to a CID Gallup poll, one of the highest in the world for a world leader — although support for him dwindled recently after his government reversed a landmark mining ban.

Still, Mr. Bukele’s approach eroded civil rights in the country, human rights experts say: Mass arbitrary arrests, extreme overcrowding at prisons, reports of torture and at least 261 prison deaths between 2022 and 2024 were documented by several groups.

How has Bukele used the prison system?

Mr. Bukele’s prisons are not typical penitentiaries. El Salvador’s gangs once used jails as operational hubs to issue orders, extort businesses on the outside and recruit new members — something also seen inside prisons across Latin America.

That no longer seems to happen “because of the extreme measures taken to control prisoners,” according to a 2023 report by Insight Crime, an organized-crime research group.

The star of Mr. Bukele’s strategy is his so-called mega prison: the Terrorism Confinement Center, known as CECOT, a hulking detention center that opened in 2023 an hour outside the country’s capital, San Salvador. The facility is big enough to hold up to 40,000 inmates, some of them as young as 12.

The vast majority of the 85,000 Salvadorans apprehended under the 2022 state of emergency — which allows for mass arrests with no due process — have essentially disappeared into the prison system, where many have been held for years without trial and without their families even knowing if they are alive.

While the imposing CECOT has garnered international attention, most prisoners are held in other, smaller facilities where “they have been subjected to cruel and inhumane treatment,” said Noah Bullock, the executive director of the Salvadoran advocacy group Cristosal, which has interviewed hundreds of detainees arrested under the state of emergency.

Cristosal and Human Rights Watch have reported that inmates were being tortured and deprived of food. Many inmates’ fates were decided in mass trials with judges whose identities were kept secret.

Who could end up in Bukele’s prisons?

The State Department said in a statement that Mr. Bukele offered to take undocumented migrants from any country, not just El Salvador, who have been convicted of crimes, including members of the MS-13 and the Tren de Aragua gangs.

And in what the State Department called “an extraordinary gesture, never before extended by any country,” it said Mr. Bukele had offered to house “dangerous American criminals, including U.S. citizens and legal residents.” Analysts say that such a move is likely to be challenged, even if it were to be embraced by the Trump administration.

“I do not think that it will stand up in the courts,” Mneesha Gellman, an associate professor of political science at Emerson College, said, citing multiple domestic and international laws that govern the treatment of both undocumented people in the United States and U.S. citizens.

However, the two governments could reach an agreement that would allow the United States to deport large numbers of people to El Salvador, including non-Salvadorans, Ms. Gellman said. The United States is eager to find places to deport migrants whose countries do not accept regular U.S. deportation flights, such as Cubans and Nicaraguans.

Whether in or out of prisons, migrants would find themselves extremely vulnerable in El Salvador.

“They would not have citizens’ rights in that country,” Ms. Gellman said, noting that migrants in El Salvador have reported experiencing abuses at the hands of criminal groups as well as state actors, such as the police and the military.

Is there any precedent for El Salvador’s offer?

In 2019, El Salvador signed an agreement with the first Trump administration to receive non-Salvadoran migrants who had been detained in the United States after U.S. officials cut off some aid to El Salvador, accusing the country of not doing enough to curb illegal migration.

It also agreed to process asylum requests to keep migrants from heading north to the United States.

Known as a “safe third country” agreement, the deal was never implemented because of the coronavirus pandemic and was eventually terminated by the Biden administration. Mr. Bukele referred to it on Monday, saying his new proposal was “more important and of a much broader scope than the agreements made in 2019.”

What could Bukele get out of this deal?

Mr. Bukele has appeared eager to strengthen his ties to the Trump administration, and the latest offer “clearly helps to consolidate this relationship between the MAGA world and El Salvador,” said Manuel Meléndez Sánchez, a Salvadoran political scientist and researcher at Harvard University.

But relations between the two government have not always been close.

In 2022, Mr. Rubio criticized Mr. Bukele during a Senate hearing, accusing him of “very openly” mocking U.S. institutions.

During his presidential campaign, even Mr. Trump took an out-of-nowhere dig at Mr. Bukele, saying he was sending “all of his criminals, his drug dealers” to the United States, and adding: “He’s trying to convince everybody what a wonderful job he does in running the country — well, he doesn’t do a wonderful job.”

In addition to currying favor with the new administration, there is also a financial incentive in El Salvador’s offer, with its approach to prisons costly to maintain.

“There’s an expense that needs to be addressed. It’s not sustainable for the Salvadoran people to maintain 2 percent of its population in prisons indefinitely,” said Mr. Bullock.

Gabriel Labrador contributed reporting from San Salvador and Michael Crowley from San José, Costa Rica.

President Trump signed an executive order on Tuesday calling for a general review of U.S. funding and involvement in the United Nations, casting uncertainty on the leadership role the United States has played as the global body’s top donor.

“I’ve always felt that the U.N. has tremendous potential,” Mr. Trump said before signing the order in the Oval Office. “It’s not living up to that potential right now.”

Mr. Trump also withdrew the United States from the U.N.’s Human Rights Council and stopped funding the U.N. agency that aids Palestinians, UNRWA, which provides critical humanitarian assistance to millions of people in war-torn Gaza. Those moves were expected because Mr. Trump had withdrawn U.S. involvement from both organizations during his first term as president.

In addition, Mr. Trump’s order called for a review of U.S. involvement in UNESCO, which protects world heritage sites, on allegations that it had exhibited what the White House staff secretary, Will Scharf, called “anti-American bias.” In handing the order to Mr. Trump to sign, Mr. Scharf said it derived from “wild disparity and levels of funding among different countries” that Mr. Trump viewed as “deeply unfair to the U.S.”

In response to the executive order, Stéphane Dujarric, a U.N. spokesman, said U.S. support for the U.N. had advanced global security and that Secretary General António Guterres “looks forward to continuing his productive relationship with President Trump and the U.S. Government to strengthen that relationship in today’s turbulent world.”

The U.N. has been bracing for Mr. Trump’s second term, having already experienced a turbulent period during his first four years in office. Mr. Guterres managed the U.N.’s then-tense relations with Washington by mostly refraining from engaging in public spats with Mr. Trump.

On the first day of his second term, Mr. Trump pulled the United States out of the World Health Organization and the Paris climate agreement.

“Trump’s attacks on UNRWA and the U.N. Human Rights Council were widely expected,” said Richard Gowan, the U.N. director of the International Crisis Group, a conflict-resolution agency. “But the knock-on effects of the administration’s aid freeze,” he added, “are making U.N. officials increasingly nervous.”

In addition to hosting the U.N. headquarters in New York City, the United States is also the agency’s top donor, contributing about 22 percent of its overall budget, followed by China (15 percent) and Japan (8 percent). For 2024, the U.S. contribution was estimated at about $3.6 billion, which goes toward the agency’s administrative and peacekeeping budget.

The United States is also a major donor to various U.N. agencies and the world body’s annual global humanitarian appeal for money to help populations during conflicts and natural disasters. In 2022, the United States contributed about $18 billion to the U.N. across the board. Last year, it paid for 47 percent, or about $14 billion, of the agency’s global humanitarian efforts.

But Mr. Trump on Tuesday criticized the U.N. for what he described as its inability to resolve conflicts raging around the world — ones that he said his administration was trying to address. The U.N. has been widely rebuked for not fulfilling its mandate to mediate and uphold peace in parts of the world.

The U.N. Security Council — a 15-member body responsible for mediating and ending conflicts — has been accused of failing to act on the wars in Ukraine and Gaza because of tensions among its five veto-holding permanent members: Britain, China, France, Russia and the United States. In the case of Ukraine and Gaza, for example, both Russia and the United States have blocked multiple resolutions that attempted to bring an end to the wars.

Mr. Trump, without naming any country, said on Tuesday that the U.N. had not been “fair to countries that deserve fairness.” He most likely meant Israel. Elise Stefanik, Mr. Trump’s pick to be the U.S. ambassador to the U.N., said during her Senate confirmation hearing that the agency had an anti-Israel bias and accused it of antisemitism.

Mr. Trump also speculated, without evidence, that many countries would leave the U.N. if the organization did not change course. He added that the United States, as the top financial backer of the U.N., was not looking to take away money, but that it wanted to push the organization to operate more efficiently.

In practical terms, Mr. Trump’s decisions on UNRWA and U.N. Human Rights Council may not have much of an immediate effect.

The Biden administration stopped funding UNRWA after Israel accused the agency of being widely infiltrated by Hamas. Two U.N. investigations found that about nine of 13,000 of its staff members in Gaza were affiliated with the militant group, and they were fired.

As for the U.N. Human Rights Council, a spokesman said the United States was not currently among the Geneva-based council’s 47 voting members, therefore the decision to withdraw had little effect on the agency’s work. The council authorizes investigations, applies pressure to hold authoritarian governments accountable and debates violations in countries like Russia, Myanmar, Iran and North Korea.

The United States gave up its membership in the council at the end of 2024, under the Biden administration. But as an observer state, it was still entitled to participate in council deliberations and could still, if it chose to, play an influential role by speaking in debates and shaping the content of council resolutions.

A critical test of the Trump administration’s intentions will come later this year, when the United States is due to undergo a council review of its human rights record, a process in which every U.N. member state has taken part. A U.S. decision not to partake in the next review, set for November, would deal a severe blow to the council’s credibility and open the way to dictatorial states to similarly avoid scrutiny.

Rights groups said that a complete withdrawal means the United States would be absent in these discussions, a notion that they said sends the wrong message.

“President Trump’s performative decision to pull the U.S. out of the H.R.C. signals to the rest of the world that the U.S. is happy to completely cede important decisions about human rights violations happening across the globe to other countries,” said Amanda Klasing, the national director of Amnesty International USA.

Nick Cumming-Bruce contributed reporting.

The Aga Khan IV, who as the leader of the world’s Ismaili Muslims fused entrepreneurship and philanthropy in becoming one of the world’s wealthiest hereditary rulers, died on Tuesday in Lisbon. He was 88.

His death was confirmed by his Aga Khan Development Network in a post on X, the social media site. No cause was given.

Urbane, cosmopolitan and often media-averse, the Aga Khan — born Prince Karim Al-Hussaini — rejected the notion that expanding his personal fortune would conflict with his charitable ventures. He said his ability to prosper complemented his duty to enhance the lives of Ismaili Muslims, a branch of the Shiite tradition of Islam with a following of 15 million people in 35 countries.

An imam, or leader of his faith, was “not expected to withdraw from everyday life,” he once said after becoming the Aga Khan. “On the contrary, he’s expected to protect his community and contribute to their quality of life. Therefore, the notion of the divide between faith and world is foreign to Islam.”

His projects included developing the island of Sardinia’s ritzy Costa Smeralda resort area, breeding thoroughbred racehorses and establishing health initiatives for the poor in the developing world.

He took issue with descriptions of his lifestyle as lavish, though he traveled on his own private jets and a luxury yacht, owned a private Caribbean island and shuttled among a variety of residences, including Aiglemont, a sprawling estate north of Paris that became the headquarters of his development network and a training center for his horses.

“The role and responsibility of an imam,” he said in a speech in 2006, “is both to interpret the faith to the community and also to do all within his means to improve the quality, and security, of their daily lives.”

Even though he had no inherited realm in the manner of other hereditary rulers, the Aga Khan’s fortune was variously estimated at $1 billion to $13 billion, drawn from investments, joint ventures and private holdings in luxury hotels, airlines, racehorses and newspapers, as well as from a kind of Quranic tithe levied on his followers.

Unusually, the Aga Khan — the name is often translated as a blend of Turkish and Persian meaning commanding chief — inherited his title from his grandfather the Aga Khan III, who bypassed his other descendants to name his grandson as his successor. With his assumption of the leadership as 49th imam of Ismaili Muslims, the Aga Khan IV took the reins of a Shia Muslim lineage that claimed descent from the Prophet Muhammad and imposed what he said were clear responsibilities on him.

At the time, he was a 20-year-old student of Islamic history at Harvard. In 1957, Queen Elizabeth II of Britain conferred on him the nonhereditary title of His Highness, a reflection of the close ties between the two dynasties, bonded in a shared fascination with fine horses.

In his will, his grandfather Sultan Mohamed Shah said he had chosen to skip a generation in part because the “fundamentally altered conditions in the world” — including advances in atomic science — required a “young man who has been brought up and developed during recent years and in the midst of the new age, and who brings a new outlook on life to his office.”

Indeed, the Aga Khan IV confronted several modern-day crises afflicting his followers, who are concentrated in Central Asia, Afghanistan, Pakistan, Iran and East Africa. Many of them faced upheavals, like the 1972 decision by the Ugandan dictator Idi Amin to expel Asians and the turmoil in Tajikistan following the collapse of the Soviet Union.

The Aga Khan was long known as a well-connected person. As such, he was able to persuade Prime Minister Pierre Elliot Trudeau of Canada, whom he had met in the 1960s, to permit thousands of Ismaili Muslims to emigrate to Canada when they were forced to leave Uganda.

His friendship with Mr. Trudeau reflected an ambiguous relationship with Canada, where he became an honorary citizen in 2010. In 2017, Mr. Trudeau’s son, Prime Minister Justin Trudeau, drew censure from Canada’s ethics commissioner after he and his family accepted the Aga Khan’s hospitality with an unannounced vacation at the prince’s private residence in the Bahamas.

The trip was deemed to represent a conflict of interest, because the Aga Khan Foundation had recently received $38 million worth of federal support from the Canadian authorities. For his part, the Aga Khan was officially exonerated.

Following the collapse of the Soviet Union, the Aga Khan’s followers in the mountainous Pamir region of Tajikistan were among those embroiled in a ruinous civil war in the 1990s against the government led by Emomali Rahmon. In response, the Aga Khan accelerated investments in power generation and a cellphone company in Tajikistan and later built health care, microfinance and other facilities, as well as the University of Central Asia in Khorog.

But the Aga Khan’s revered status among Ismaili Muslims, living mainly in Tajikistan’s Gorno-Badakhshan Autonomous Province, reportedly stirred resentments and resistance among the country’s secular leaders, who sought to block demonstrations of support for the Aga Khan.

Prince Karim Al-Hussaini was born in Geneva on Dec. 13, 1936. He was the eldest son of the noted playboy Prince Aly Khan and his first wife, Joan (Yarde-Buller) Khan, a descendant of British aristocracy. His younger brother, Amyn Aga Khan, was born the following year.

In 1949, their parents divorced, and Prince Aly went on to marry the American actress Rita Hayworth, with whom he had a daughter, Princess Yasmin Aga Khan.

Known in his youth as Prince Karim, the Aga Khan grew up in Nairobi, Kenya, before attending school at the exclusive Institut Le Rosey in Geneva. In his late 20s, he competed for pre-revolutionary Iran in skiing at the 1964 Olympics in Innsbruck, Austria.

He went on to Harvard, where he was studying Islamic history when he became Aga Khan IV on the death of his grandfather.

“It was a shock,” he said in an interview in 2013 with Vanity Fair magazine, “but I don’t think anyone in my situation would have been prepared.”

His new status, he said, meant that the course of his life was henceforth set on immutable coordinates. “I was an undergraduate who knew what his work for the rest of his life was going to be,” he said.

Some of his followers ascribed divine status to him, but he rejected such notions of godliness.

In 1969, he married Sally Croker Poole, a British model and former debutante who became Salima Aga Khan. The couple had three children, Princess Zahra, Prince Rahim and Prince Hussain, before they divorced in 1995. All three siblings went on to work in the Aga Khan’s organizations.

Three years later, the Aga Khan married Gabriele (Thyssen) zu Leiningen of Germany, who became Inaara Aga Khan. They had a son, Prince Aly Muhammad. The couple broke up a few years later and spent a decade negotiating a divorce settlement said to be worth about $60 million when adjusted for inflation.

He is survived by his children; his brother, Prince Amyn Muhammad; his half sister, Princess Yasmin; and four grandchildren.

Over the years, the Aga Khan’s business ventures were eclectic. He was a prime mover in the 1960s in building the resort of Porto Cervo, complete with a yacht club and polo tournaments, as part of the development of Sardinia’s northern Costa Smeralda as a playground for the superrich. He showed a liking for Maserati sports cars, but he also invested in the developing world in basic industries that made fishnets, plastic bags and matches.

In Uganda, following the overthrow of Idi Amin and the later rise of Yoweri Museveni, he joined private equity giants like the Blackstone Group in a $750 million hydroelectric scheme.

In 1960, Prince Aly, the Aga Khan’s father, died in a car crash at Suresnes, outside Paris, and his children inherited his lucrative equestrian empire, which included nine farms in Ireland and France. “The three of us found ourselves with this family tradition none of us knew the first thing about,” he told Vanity Fair in 2013.

Since then, the Aga Khan had owned, trained and bred many champion horses. In France, his filly Valyra won the prestigious Prix de Diane in 2012, to establish a new owners’ record of seven wins. In the 1980s, his stallion Shergar was abducted in Ireland and never seen again. (He refused to pay a ransom demand.)

“I’ve come to love it — it’s so exciting, a constant challenge,” he once said of the equestrian business. “Every time you sit down and breed, you are playing a game of chess with nature.”