Three US aircraft came under fire from unidentified forces yesterday while trying to evacuate Americans from the spiralling conflict in South Sudan.

The US military said four of its members were wounded in the attacks.

The US aircraft came under fire while approaching the evacuation site, the military's Africa Command said in a statement. "The aircraft diverted to an airfield outside the country and aborted the mission," it added.

The statement said all of the three Osprey CV-22 aircraft involved in the mission had been damaged.

Nearly a week of fighting in South Sudan threatens to drag the world's newest country into a Dinka-Nuer ethnic civil war just two years after it won independence from Sudan with strong support from successive US administrations.

Consequently, US President Barack Obama warned that any move to take power by military means would lead to an end of US and international community support for South Sudan.

The United Nations mission in South Sudan said one of four UN helicopters sent to Youai, in Jonglei state, had come under small-arms fire on Friday. No crew or passengers were harmed.

Hundreds of people have been killed in the fighting between Dinka loyalists of President Salva Kiir and Nuer supporters of former Vice-President Riek Machar, who was sacked in July and is accused by the government of trying to seize power.

Fighting has spread from the capital, Juba, to vital oilfields and the government said a senior army commander had defected to Machar in the oil-producing Unity State.

The German military said it had evacuated 98 people, including Germans and other nationals, from South Sudan by air to neighbouring Uganda.

The German ambassador to South Sudan was among them, the Foreign Ministry in Berlin said.

After meeting African mediators on Friday, Mr Kiir’s government said on its Twitter feed that it was willing to hold talks with any rebel group. The US is sending an envoy to help find a negotiated solution.