El Salvador's President Nayib Bukele has offered for illegal immigrants – of any nationality – facing deportation in the U.S. to be booked in his country's prison system in exchange for a fee.

This proposal comes after Secretary of State Marco Rubio met with Bukele at his lakeside country house outside San Salvador on Monday.

"We have offered the United States of America the opportunity to outsource part of its prison system," Bukele wrote on X Monday night. "We are willing to take in only convicted criminals (including convicted U.S. citizens) into our mega-prison (CECOT) in exchange for a fee. The fee would be relatively low for the U.S. but significant for us, making our entire prison system sustainable."

Rubio said the Salvadoran president "has agreed to the most unprecedented, extraordinary, extraordinary migratory agreement anywhere in the world."

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"We can send them, and he will put them in his jails," Rubio told reporters, referring to illegal immigrants behind bars in U.S. prisons. "And, he’s also offered to do the same for dangerous criminals currently in custody and serving their sentences in the United States, even though they’re U.S. citizens or legal residents."

While Bukele did extend the offer to include violent American criminals, it is highly unlikely that part of the offer would actually happen, since it is illegal to deport U.S. citizens. A U.S. official said the Trump administration has no plans to deport American citizens, but noted that Bukele's offer was significant.

The proposal with El Salvador, known as a "safe third country" agreement, could potentially be an option for Venezuelan gang members convicted in the U.S. if Venezuela refuses to accept them, and Rubio said Bukele offered to accept detainees of any nationality.

Bukele also said he would take back all Salvadoran MS-13 gang members in the U.S. illegally, and promised to accept and incarcerate criminal illegal aliens from any country, especially those affiliated with Venezuela's Tren de Aragua gang.

Manuel Flores, the secretary general of the leftist opposition party Farabundo Martí National Liberation Front, argued that the "safe third country" plan would paint the region as the U.S. government's "backyard to dump the garbage."

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Rubio was visiting El Salvador to push for more help in supporting President Donald Trump's mass deportation plan. He arrived in San Salvador shortly after watching a U.S.-funded deportation flight carrying 43 illegal immigrants leave from Panama for Colombia.

The deportation flight had 32 men and 11 women detained by Panamanian authorities after illegally crossing the Darien Gap from Colombia. The State Department said the deportations send a message of deterrence.

"Mass migration is one of the great tragedies in the modern era," Rubio said afterward. "It impacts countries throughout the world. We recognize that many of the people who seek mass migration are often victims and victimized along the way, and it’s not good for anyone."

Rubio's trip comes during a sweeping freeze on U.S. foreign assistance and stop-work orders that have shut down taxpayer-funded programs targeting illegal immigration and crime in Central America. The State Department said that the secretary had approved waivers for certain critical programs in countries he is visiting.

The secretary will continue to urge foreign leaders to do more to help the U.S. combat illegal immigration, including in his next stops in Costa Rica, Guatemala and the Dominican Republic, which are part of his five-nation Central American tour following the visits to Panama and El Salvador.

The Associated Press contributed to this report.