The United States is being asked to explain why it appears to be deporting migrants from as far away as Vietnam and Cuba to South Sudan, a chaotic country that's once again in danger of collapsing into civil war.

The United Nations rights chief urged on Friday for warring sides in South Sudan to pull back from the brink, warning that the human rights situation risks further deterioration as fighting intensifies.

A federal judge ruled late Tuesday that U.S. officials must retain custody and control of migrants apparently removed to South Sudan in case he orders their removals were unlawful.

Doctors Without Borders, known by its French initials MSF, has warned of a looming “health catastrophe” among South Sudanese refugees in Ethiopia, citing surging cholera cases and widespread malnutrition in overcrowded camps near the border.

South Sudan's President Salva Kiir has reshuffled the senior leadership in the ruling party, according to an official decree, as the country faces fresh fighting between rival armed factions and widespread speculation about Kiir's succession plans.