The memo instructs ICE employees on how to deport people to countries other than their country of origin, in some cases in as little as six hours.

"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.