Officials have said most of the people sent to the U.S. base are members of a Venezuelan gang but have not offered evidence to support that claim.

The 40 men were transported to Louisiana as the detention operation faces a number of logistical and legal hurdles.

The Trump administration has deported hundreds of migrants while refusing to reveal their identities or the evidence against them, prompting complaints from the migrants’ families and from critics who say the administration is trampling on civil liberties.