Fighting between opposing ethnic military groups in South Sudan has spread from the capital to the rural state of Jonglei, and the death toll has reportedly reached 500.
About 20,000 people have sought refuge at UN facilities in Juba, the capital, since fighting started on Sunday, and on Tuesday the United States ordered its citizens to leave the country immediately.
President Salva Kiir said in an address to the nation he had foiled a coup attempt by a group of soldiers loyal to former vice president Riek Machar, who is now the subject of a manhunt by Sudan's military. Foreign minister Barnaba Marial Benjamin said that Mr Machar is believed to have fled Juba and that the government believes he is in hiding.
"If he wants to become president, he needs to wait for elections," Mr Benjamin said. "He wants to be president, but in the wrong way."
At least 10 political leaders have been arrested over their roles in the coup.
The clashes are pitting soldiers from the majority Dinka tribe of Kiir against those from Mr Machar's Nuer ethnic group.
Casie Copeland, the South Sudan analyst for the International Crisis Group, said key Nuer leaders in the army are defecting in Jonglei, in an escalation of the conflict.
"The situation is no longer contained to Juba. This extension of conflict to the state-level is deeply concerning and poses serious challenges for ongoing efforts to reduce hostilities," she said.
Tension had been mounting in South Sudan since Mr Kiir fired Mr Machar as his deputy in July, sparking concerns about possible tribal clashes. Mr Machar said if the country is to be united it cannot tolerate a "one man's rule or it cannot tolerate dictatorship." His removal, part of a wider dismissal of the entire cabinet, followed reports of a power struggle within the ruling party.
The coup attempt took place on Sunday when some soldiers raided the main army barracks' weapons store in Juba but were repelled by loyalists, sparking gunfights across the city. The government has given few details, raising questions about what sparked the violence.
South Sudan has been plagued by ethnic violence since it peacefully broke away from Sudan in 2011 after decades of civil war.