White House Press Secretary Karoline Leavitt said Tuesday the first flights of undocumented immigrants from the U.S. to Guantánamo Bay in Cuba were underway—following an escalation of arrests across the country as part of what President Donald Trump has promised would be the “largest deportation operation” in U.S. history.

U.S. officials say the first military aircraft carrying detained migrants to Guantanamo Bay is expected to depart on Tuesday.

As tents went up in Guantanamo Bay, Cuba to hold migrants, attorneys at the Department of Homeland Security and Pentagon were still trying to determine whether it was legal to take the unprecedented step of flying migrants from the US southern border to the facility,