The United States evacuated more embassy staff on Friday from South Sudan's capital Juba due to worsening security in the country, where clashes between rebels and the army risk turning into full-blown civil war.
The fighting, which began on Dec. 15, has split the world's newest state along ethnic lines, between President Salva Kiir's Dinkas and former vice president Riek Machar's Nuer group, and raised fears of regional instability.
Kiir's government and the rebels have sent negotiators to neighbouring Ethiopia for peace talks. They have yet to meet face-to-face but have separately met mediators from the East African bloc IGAD.
"We are not suspending our operations. We are just minimising our presence," Susan Page, the U.S. ambassador to Juba, told Reuters.
An emergency message to U.S. citizens on the embassy's website said the move was due to a "deteriorating security situation". It said there would be an evacuation flight on Friday arranged by the U.S. State Department.
Kiir's government and the rebels loyal to Machar have agreed to a ceasefire, mediators say, but there is no agreement yet on a starting date and some diplomats say both sides still seem more intent on manoeuvring for military advantage.
Rebel spokesman Moses Ruai Lat, based in the northern state of Unity, said on Friday his comrades, who have seized control of Jonglei state's capital Bor, were now marching towards Juba and were already "close" to the capital.
His comments came a day after the Sudan People's Liberation Army (SPLA), which is loyal to the government, said its forces were advancing on Bor, a strategic town some 190 km (118 miles) by road north of Juba, to meet rebel militia heading south.
Such reports will fan concerns of a further escalation in violence that has already killed 1,000 people in South Sudan, a country the size of France with nearly 11 million people that seceded from Sudan in 2011.
Kiir has accused his long-term political rival Machar, whom he sacked in July, of starting the fighting in a bid to seize power. Machar denies the claim.
In the Ethiopian capital Addis Ababa, the peace negotiations have got off to a slow start.
"Both delegations are meeting the mediators separately," said Dina Mufti, a spokesman for Ethiopia's foreign ministry. "We hope to bring both sides into face-to-face talks soon."