Military spokesman Philip Aguer said on Thursday that soldiers had lost control of Bor, which lies 200 kilometers (125 miles) north of the capital Juba. Bor is the capital of the eastern state of Jonglei, one of the most volatile regions in South Sudan.

"Our soldiers have lost control of Bor to the force of [deposed Vice-President] Riek Machar late on Wednesday," Aguer said.

"There was shooting last night ... we don't have information on casualties or the displaced in the town, as operations are ongoing."

Aguer said authorities in Bor were not answering their phones, leading the government to suspect they had defected.

The fighting follows a reported coup attempt against the government on Sunday in Juba, which killed a number of people, including soldiers loyal to either president Salva Kiir or his former deputy Machar, who was sacked from the government in July.

Kiir has blamed Machar for being behind the coup attempt. Machar, who is on the run, has denied this and accused Kiir of using it as an excuse to remove his political rivals.

"There was no coup. What took place in Juba was a misunderstanding between presidential guards within their division. It was not a coup attempt. I have no connection with or knowledge of any coup attempt," Machar told the Sudan Tribune on Wednesday.

Machar added in the interview that Kiir was continuing to violate the constitution and "was no longer a legal president."

"We don't want him the president of South Sudan anymore."

UN: 'hundreds' dead

Fears are growing in the international community of a return to civil war in South Sudan, with the fighting pitting soldiers from Kiir's Dinka tribe against Machar's Nuer ethnic group.

South Sudan, the world's youngest nation, has experienced ethnic tensions since its independence from Sudan in 2011.

On Wednesday, the UN said military sources put the death toll since Sunday at between 400 and 500. It said the fighting has forced thousands of people to seek refuge at UN facilities (seen above).

Germans have been among those evacuated, including DW staff members. The German newsmagazine Spiegel Online reported that Lieutenant General Hans-Werner Fritz, the chief of the German Bundeswehr Operations Command, had been unable to leave South Sudan because of a delayed flight.

Kiir has also appeared to extend an olive branch to Machar, with the news agency AFP quoting the president on Wednesday telling reporters: "I will sit down with him - Riek - and talk ... but I don't know what the results of the talks will be."

jr/kms (AFP, AP, dpa)