Updated

The United Nations Mission in South Sudan says it is relocating all non-critical staff from the capital, Juba, to Uganda amid escalating violence as the country's military battles rebel forces.

The mission said in a Twitter update Sunday that all remaining civilian staff in Bor — the Jonglei state capital that has been the scene of fierce fighting — had been evacuated to Juba.

On Saturday gunfire hit three U.S. military aircraft trying to evacuate American citizens in Bor, wounding four U.S. service members in the same region gunfire downed a U.N. helicopter on Friday.

The latest violence in the world's newest country has killed hundreds and has world leaders concerned about war.

The U.N. chief Sunday urged South Sudan's leaders "to do everything in their power" to stop the violence.