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.

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.

After years of gradual progress toward stability, a succession battle is pushing the country to the precipice of another full-blown civil war.