Five immigrants deported by the United States to the small southern African nation of Eswatini under the Trump administration’s secretive third-country program are in prison, where they will be held in solitary confinement for an undetermined time.

The U.S. Homeland Security Department said on Tuesday a deportation flight carrying immigrants from different countries had landed in Eswatini, in a move that follows the U.S. Supreme Court lifting limits on deporting migrants to third countries.

Eswatini, formerly known as Swaziland, is the only nation in Africa where the monarch retains full executive power