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.

Eswatini says it is holding the men in correctional facilities until they can be sent to their home countries, after it became the latest nation to accept third-country deportees from the U.S.

The administration has made the practice of third country deportations central to its sweeping immigration policy.