JUBA, South Sudan (AP) -- At least 500 people, most of them soldiers, have been killed in South Sudan since Sunday, a senior government official said, as an ethnic rivalry threatened to tear apart the world's newest country.
The clashes apparently are pitting soldiers from the majority Dinka tribe of President Salva Kiir against those from ousted Vice President Riek Machar's Nuer ethnic group, raising concerns the violence could degenerate into a civil war.
Fighting spread on Wednesday to Jonglei, the largest state in South Sudan, where troops loyal to Machar were said to be trying to take control of Bor, the state capital.
Machar himself is the subject of a manhunt by the country's military after he was identified by Kiir as the leader of an alleged coup attempt on Sunday. Machar has denied he was behind any coup attempt.
Barnaba Marial Benjamin, the foreign minister, told The Associated Press late Wednesday that there was heavy fighting in Bor, but he denied renegade soldiers had overtaken it.
"There is fighting there, but (government forces) haven't lost control of the town," he said, accusing Machar of actively mobilizing soldiers to mutiny against the government.
Col. Philip Aguer, the South Sudanese military spokesman, said there was fighting Wednesday among troops in Jonglei state but that it was not clear "who is fighting who."
He said military officials in Juba, the capital of South Sudan, were trying to confirm reports of defections in Bor.
At least 19 civilians have been killed in violence in Bor, said Martin Nesirky, a spokesman for the U.N. secretary-general's office, citing figures from the South Sudan Red Cross. He said tensions were also on the rise in the states of Unity and Upper Nile.
Tensions have been mounting in South Sudan since Kiir fired Machar as his deputy in July. Machar has said he will contest the presidency in 2015.
Kiir told a news conference in Juba late Wednesday that he was willing to enter talks with Machar, a rival for power within the ruling Sudan People's Liberation Movement party.
"I will sit down with him so that we talk, but I cannot tell what the outcome of such talks would be," he said.
U.N. chief Ban Ki-moon told reporters Wednesday that South Sudan was experiencing a political crisis that "urgently needs to be dealt with through political dialogue." Ban said he urged Kiir "to resume dialogue with the political opposition."
South Sudan has been plagued by ethnic violence since it peacefully broke away from Sudan in 2011 after decades of civil war. The fighting began Sunday in Juba, but it was mostly calm Wednesday.
Some of the victims "were shot in the bushes" around Juba, Information Minister Micheal Makuei Lueth said, citing a report from the minister of defense. He said up to 700 others had been wounded.
The violence has forced about 20,000 people to seek refuge at U.N. facilities in Juba since Sunday.
Casie Copeland, the South Sudan analyst for the International Crisis Group who is in Juba, said key Nuer leaders in the army were defecting in Jonglei but that "events that led to Sunday's fighting remain unclear."
Toby Lanzer, the U.N.'s humanitarian coordinator in South Sudan, said in a Twitter post that thousands of civilians in Jonglei had sought refuge at a U.N. facility there.
A dusk-to-dawn curfew was in place in Juba, and an AP reporter saw a heavy police and army presence on its streets.
On Tuesday the United States ordered its citizens to leave South Sudan immediately. The U.S. diplomatic mission in Juba said on Twitter that an evacuation flight was full Wednesday and it would advise if there was another flight Thursday.
In a BBC interview Wednesday, Machar denied any link with the current fighting and blamed it on a conflict between members of the presidential guard. He added that government troops used the incident to arrest some of his supporters Monday and that he himself escaped.
"Someone wanted to frame me," he said. "I had to flee. They are hunting me down."
Benjamin, the foreign minister, insisted that Machar had orchestrated the violence in a bid to take power. "If he wants to become president, he needs to wait for elections," Benjamin said.
At least 10 political leaders have been arrested over their roles in the alleged coup, the government said.