According to US media reports, all the remaining migrants detained there were transported to another immigration facility in Louisiana.

In February, a separate group of migrants were abruptly moved from the facility after only a few weeks.

Shortly after taking office in January, President Donald Trump ordered that an existing facility used to hold migrants in Guantanamo Bay be expanded to hold some 30,000 people.

But so far, only a few hundred appear to have been sent there.

It is unclear why the Department of Homeland Security (DHS) has brought the latest group of migrants held at Guantanamo back to the US. It declined the BBC’s request for comment.

The move, however, comes just days before a federal judge is due to hear a legal challenge on the legality of the federal government’s move to send migrants to Guantanamo, in a lawsuit filed by a coalition of human rights groups, including the American Civil Liberties Union.

US media report that 40 migrants were flown from Guantanamo to Alexandria in Louisiana on Tuesday and Wednesday, where Immigration and Customs Enforcement (Ice) has a processing facility.

A facility used to hold migrants at Guantanamo, called the Guantanamo Migrant Operations Center, has been used by both Republican and Democratic administrations for decades – a practice long-criticised by some human rights groups.

Another facility, a high-security military prison once used to house detainees suspected of terrorism offences, is also located at Guantanamo.

The Washington Post reports that as of 10 March, 23 migrants were being held in the military detention facility, while 17 others were detained in the Migrant Operations Center, citing a Pentagon official.

Last week, a defence official told the BBC the US military had last received a request from DHS to transport undocumented migrantsto Guantanamo Bayon 1 March, adding that it stood ready to assist if additional flights are requested.

The expansion of the existing migrant centre at Guantanamo is part of a wider effort to dramatically overhaul the US immigration system, which has included promises of mass deportations.

At a signing ceremony early in his term, Trump said that the facility would largely be used to hold undocumented migrants deemed to be dangerous criminals or national security risks.

“Some of them are so bad we don’t even trust the countries to hold them, because we don’t want them coming back,” he said of migrants. “So we’re going to send them to Guantanamo… it’s a tough place to get out.”

The administration’s “border tsar”, Tom Homan, defended the use of the facility as recently as last week and said that plans for its expansion were still under way.

On 4 March, for example, he said the facility was “the perfect place for the worst of the worst” and that plans for its expansion were still in place.

Court documents filed late last week show that about 300 migrants from 27 countries have gone through the facility.

Two separate lawsuits have been filed challenging migrant detention in such facilities.

In one case, a coalition of legal aid organisations is seeking a court order allowing detainees at the facility access to attorneys, including in-person visits.

A second lawsuit directly challenges the legality of transferring migrants detained in the US to Guantanamo.

A brief statement from the Department of Homeland Security (DHS) said the detainees were part of the Tren de Aragua – a gang that originated in Venezuela’s prisons.

Ten detainees were flown from the Fort Bliss Army base near the Texas border to the US Navy base in Cuba on Tuesday afternoon, the BBC’s US partner CBS News reported, citing multiple US officials.

Last week, Trump ordered that an existing migrant detention facility at the base be expanded to hold some 30,000 people.

He said that would double the US capacity to hold undocumented migrants.

The move is part of Trump’s effort to crack down on undocumented migrants in the US after his return to office. He has promised arrests and mass deportations.

In Tuesday’s brief statement, DHS Secretary Kristi Noem said: “President Donald Trump has been very clear: Guantanamo Bay will hold the worst of the worst. That starts today.”

The department published several photographs of the detainees being taken on board the plane. Two officials told CBS that the group was considered “high-threat”.

Trump ordered that the Tren de Aragua be designated as a foreign terrorist organisation last month, as part of a directive targeting gangs and cartels.

The existing facility – Guantanamo Migrant Operations Center (GMOC) – has been used by both Republican and Democrat administrations to house migrants for decades. It has principally held migrants picked up at sea.

The expanded facility would be run by Immigration and Customs Enforcement (ICE), Trump’s border tsar Tom Homan said last week.

Announcing his plan last week that the facility be expanded, Trump said: “Some of them (the migrants) are so bad we don’t even trust the countries to hold them, because we don’t want them coming back.

“So we’re going to send them to Guantanamo… it’s a tough place to get out.”

US military personnel travelled to Guantanamo Bay at the weekend to assemble tents to house migrants sent to the base, the New York Times and CNN reported.

Last year, the International Refugee Assistance Project (IRAP) accused the US government of secretly holding migrants at the base in “inhumane” conditions indefinitely.

The administration of Joe Biden, who was then president, responded that the location was “not a detention facility and none of the migrants there are detained”.

The GMOC is separate to the military prison on Guantanamo which has, for years, held detainees taken into US custody after the 9/11 attacks.

The Cuban government quickly condemned news of the immigration facility’s expansion last week, with President Miguel Díaz-Canel calling it “an act of brutality”.

It has long considered Guantanamo Bay to be “occupied” and has denounced the existence of a US naval base on the island ever since Fidel Castro swept to power in 1959.

The move has left 15 detainees in the prison in Cuba – the smallest number at any point in its history.

In a statement, the Department of Defense thanked Oman for supporting US efforts “focused on responsibly reducing the detainee population and ultimately closing” the facility.

None of the men captured after the 9/11 terror attacks had been charged with any crimes in their more than two decades in detention.

The transfer, which reportedly happened in the early hours on Monday, comes days before the accused mastermind of the 11 September 2001 attacks on the US, Khalid Sheikh Mohammed, is scheduled to plead guilty, following a deal with federal officials to avoid the death penalty.

Monday’s transfer of the Yemeni detainees is the largest to a single country at one time under President Joe Biden.

Efforts to resettle the group in Oman began years ago, but the US has said that Yemen, which is locked in a civil war, was too unstable for repatriation.

Those transferred from Guantanamo include Moath al-Alwi, who was cleared for release in 2022 and had become known for building model boats with objects found at the prison, and Shaqawi al Hajj, who went on repeated hunger strikes to protest his detention.

The men were cleared for transfer by federal national security review panels, which determined that doing so was “consistent with the national security interests of the United States”, the Defense Department said.

The transfer came less than a week after Ridah Bin Saleh al-Yazidi, one of the prison’s original detainees in January 2002, was repatriated to Tunisia.

The Defense Department said three of the 15 remaining detainees also are eligible for transfer.

The military prison is part of a US naval base complex in southeastern Cuba. It was established by the Bush administration in 2002, following the 9/11 attacks, to hold suspects captured in counter-terrorism operations. At its peak, it held about 800 detainees.

Controversy has centred around the treatment of detainees and how long they were held without being charged.

As president, Barack Obama pledged to close the prison during his terms. He said the prison is contrary to US values, undermining the nation’s standing in the world – a standing based on support for the rule of law.

Obama, who left office in 2017, also argued that its existence harms partnerships with countries needed to help the US fight terrorism and that it helps fuel the recruitment of jihadists.

But while in office, Obama faced opposition in Congress to shuttering the prison – some of it due to questions about what would happen to the existing prison population. He transferred or ordered the release of more than 100 detainees to other countries.

US Congress has not allowed the transfer of detainees to US states and has blocked their transfer to certain countries, including those with ongoing conflicts like Yemen.

Efforts to lower the prison’s population and close it halted under Donald Trump who signed an executive order to keep it open during his first term. Trump said efforts to release detainees or close the facility made the US look weak on terrorism.

Since taking office in 2021, President Joe Biden has worked to remove more detainees from the facility in hopes of shuttering it – though that appears unlikely before Trump takes office later this month.

He was found eligible for transfer from the detention facility after a “rigorous interagency review process”, a press statement said.

The Pentagon did not say if Mr Yazidi had accepted any guilt.Since 2002, the Guantanamo Bay detention facility has been used to hold what the US describes as captured unlawful combatants during America’s “war on terror”.

The camp is part of a US naval base complex in south-eastern Cuba.

According to an unconfirmed report by the New York Times, Mr Yazidi was never charged and was approved for transfer more than a decade ago.

The newspaper also said he had been at Guantanamo Bay since the facility was first set up in 2002.

According to Monday’s Pentagon statement, 26 detainees remain at Guantanamo Bay, of whom 14 are eligible for transfer.

Earlier in December, the Pentagon announced that the US had repatriated three other detainees, the Associated Press news agency reported.

The camp was established by the Bush administration to detain the most dangerous suspects for interrogation and the prosecution of war crimes.

Controversy has centred around the period of time detainees have been held without charge and the use of interrogation techniques.