South Sudan's government says it has lost control of a town north of the capital, Juba, as fighting among the country's armed forces stretched into a fifth day.
Government officials say rebelling soldiers seized control of Bor, where the United Nations reported fighting broke out Wednesday at a military camp. The South Sudan Red Cross says 19 civilians have been killed in the town.
Meanwhile, the country's information ministry says security forces are in "absolute control" of the situation in Juba. The government says 500 people have been killed there, with at least another 700 wounded since clashes began Sunday.
President Salva Kiir blames the violence on an alleged coup attempt by forces loyal to former vice president Riek Machar, whom he fired in July. Mr. Kiir said Wednesday he is willing to hold talks with Machar.
Observers have raised concerns that a rift between Machar, from the Nuer ethnic group, and Mr. Kiir, a Dinka, could fuel already-chronic tribal violence in South Sudan.
Human Rights Watch says South Sudanese soldiers may have specifically targeted people from the Nuer ethnic group during this week's fighting in Juba. The group also said there are reports that Nuer solders had targeted ethnic Dinkas in Juba and Bor.
In another development, top ministers from the regional Intergovernmental Authority on Development group are traveling to South Sudan on a peace mission.
The group was instrumental in mediating a 2005 agreement that ended Sudan's civil war with what was then its southern region.
U.N. Secretary-General Ban Ki-moon has urged the president to engage with his opponents and cooperate with the United Nations.
"This is a political crisis, and urgently needs to be dealt with through political dialogue. There is a risk of this violence spreading to other states, and we have already seen some signs of this."
Mr. Ban said Wednesday that as many as 20,000 people have take refuge with the U.N. mission in the capital, Juba.