Donald Trump has sent accused Venezuelan gang members to a notorious mega-jail in El Salvador, invoking the 1798 Alien Enemies Act which gives the president power to order the detention and deportation of natives or citizens of "enemy" nations without usual processes.

As ACLU attempts to remove more Venezuelan detainees, government lawyers say the administration reserves the right to have removal flights Saturday.

The case is one of several challenging moves by the Trump administration to cancel the temporary legal status of hundreds of thousands of people.