Thousands of undocumented migrants — including British citizens — are reportedly set to be detained at Guantanamo Bay, as part of Donald Trump’s renewed immigration clampdown, reports The Telegraph.

At least 9,000 migrants, some from Europe, will be transferred to the notorious detention camp within days, according to reports in the United States. The plan marks the first large-scale use of the facility for this purpose since Trump’s announcement in January that 30,000 people could be held there.

Guantanamo Bay, located in Cuba, was previously used to imprison combatants detained during the George W. Bush administration’s “war on terror” following the 9/11 attacks.

Now, it appears the controversial site is being reactivated to house undocumented migrants, at least temporarily, before they are deported to their home countries.

According to documents seen by Politico, the intention is to hold those transferred for a short period. Guantanamo currently holds around 500 people.

The White House says the move is aimed at easing overcrowding in U.S. detention centres, as the administration pursues a target of 3,000 immigration-related arrests a day. But critics say the real motive is to intimidate would-be migrants.

“The message is to shock and horrify people, to upset people,” one State Department official told Politico.

Reports say some 800 Europeans are among those slated for transfer — including citizens of Britain and France — in a move that has alarmed European diplomats, who have traditionally worked closely with Washington on migrant repatriations.

The American Civil Liberties Union (ACLU) is already challenging the policy in court, saying detainees face “dire conditions” inside the camp, including rodent infestations, insufficient food, and no regular change of clothes.

In its writ, the ACLU accused the administration of using Guantanamo “to frighten immigrants, deter future migration, induce self-deportation, and coerce people in detention to give up claims against removal and accept deportation elsewhere”.

The U.S. Justice Department rejected the claims, insisting the camp is simply being used as a temporary staging post.

The State Department has confirmed that “illegal aliens” are being sent to Guantanamo “as a temporary measure” but declined to comment on whether specific governments, including Britain’s, had been consulted about the move.

This isn’t the first time Britons have been detained at Guantanamo Bay. Nine UK citizens were held there during the early 2000s. Five were returned home in March 2004, while another nine UK residents — who did not hold citizenship — were also detained at the facility.

The unprecedented revival of Guantanamo as part of the immigration crackdown is already generating diplomatic tensions and legal challenges, with pressure mounting on the White House to justify the decision as more details emerge.