"The third countries that have received or been about to receive third-country deportees so far—El Salvador, Libya, South Sudan, now Eswatini—are marked by serious pre-existing human rights violations. This is a recipe for prolonged arbitrary detention or worse."

On board the flight were five deportees from Vietnam, Jamaica, Laos, Cuba and Yemen who have been convicted of crimes ranging from child rape to murder, US Homeland Security Department Assistant Secretary Tricia McLaughlin said in an online post.

The U.S. has already deported eight men to another African country, South Sudan, after the Supreme Court lifted restrictions on sending people to countries where they have no ties.