Fighting in South Sudan is escalating into a civil war with the rebel soldiers taking over Bor, a key town some 200kms north of the capital Juba.

This comes just three days after President Salva Kiir told the media that soldiers loyal to sacked vice president Riek Machar had tried to stage a coup in Juba.

Up to 500 people are believed to have died in the fighting that broke out on Sunday night.

Col. Phillip Aguer, the South Sudan army—SPLA spokesperson, is quoted by the BBC saying government soldiers have lost control of Bor to the forces loyal to Dr Riek Machar.

President Kiir has accused Machar, whom he sacked in July this year, of staging a coup.

Dr Machar denies the claim and instead accuses Kiir of orchestrating ethnic violence to hide his own leadership failings.

The United Nations has called for political dialogue to end the crisis, and Secretary General Ban Ki-moon said he has asked Ugandan President Yoweri Museveni to mediate. More than 20,000 people have taken refuge at the UN compounds in Juba.

The Sudan Tribune, a newspaper in South Sudan quotes President Kiir as saying he is ready for dialogue with his former deputy.

Britain and the US have both sent planes to airlift their nationals out of the country as the situation gets out of hand. On Wednesday the mayor of Bor, Nicholas Nhial Majak, told the BBC’s Focus on Africa programme that violence had spread there from Juba. Bor is the capital of Jonglei state, and is seen as one of the most volatile areas of South Sudan.

Col Aguer told reporters that there was fighting throughout the night as renegade officers fought with troops still loyal to President Kiir.

He added that government officials in the town were not answering their phones and were believed to have defected to the rebels’ side.

Tensions are also said to be high in the states of Unity and Upper Nile, according to Aguer.

The UN has expressed fears of a civil war between the Dinka and the Nuer, the two biggest ethnic tribes in a country that only got self-rule two years ago.

President Kiir hails from the Dinka, while Dr Machar is a Nuer. But presidential spokesman Ateny Wek Ateny has told the BBC that while it was likely that civilians had been caught in the fighting, no-one was targeting ethnic groups.