South Sudan's former vice president has called for the overthrow of President Salva Kiir, as tension and violence continue to rise in Africa's newest country.
Riek Machar told Radio France Internationale on Thursday that he would like to see a "palace revolution" in which the military topples the head of state.
Mr. Kiir had accused Machar of launching a coup attempt earlier this week with an attack on army headquarters in the capital, Juba. That fighting set off violence that the government says has killed some 500 people and wounded 700 others.
Thursday, the government said rebelling soldiers had seized control of Bor, a town north of Juba.
The government insisted it was in total control of Juba, saying the airport had reopened and that government ministries are operating.
However, the U.S. embassy went ahead with an evacuation flight for U.S. citizens who want to leave the country.
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.
In a VOA interview, Human Rights Watch Africa analyst Leslie Lefkow said South Sudanese soldiers may have specifically targeted people from the Nuer ethnic group during this week's fighting in Juba.
"We've spoken to a lot of people in Juba who were witnesses of what has been happening over the last few days and people have told us really horrifying accounts of civilians - men, women and children - who were in their houses, in their compounds, hiding from the fighting, and who were actively sought out by soldiers coming into their homes, shooting them, often asking people whether they were Dinka or Nuer."
Human Rights Watch also said there are reports that Nuer soldiers had targeted ethnic Dinkas.
The government denied there was an ethnic element to what it describes as Machar's "aborted coup."
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.
President Kiir said Wednesday he is willing to hold talks with Machar. 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.