A group of 238 alleged members of the Venezuelan gang Tren de Aragua and 23 members of the international MS-13 gang were sent to the notorious Terrorism Confinement Center (Cecot).
Neither the US government nor El Salvador has identified the detainees, nor provided details of their alleged criminality or gang membership.
Meanwhile, the White House has denied an accusation from rights groups that it flouted due process by defying a judge's order while carrying out deportations at the weekend.
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