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.