Negotiators for the South Sudan government and rebels had not met face-to-face but were meeting mediators in Addis Ababa, the BBC reported Friday.
The U.S. State Department said in a release staffing at the U.S. Embassy in Juba, South Sudan's capital, had been further reduced.
"As a result of this drawdown, the U.S. Embassy in Juba will not be able to provide consular services to U.S. citizens in South Sudan," the State Department said in a statement. "The U.S. Embassy in Nairobi, Kenya, will provide consular services for U.S. citizens in South Sudan until further notice."
"We continue to strongly recommend that U.S. citizens in South Sudan depart immediately."
At least 1,000 people have died since fighting erupted last month between supporters of President Salva Kiir and those of Riek Machar, who Kiir sacked during the summer. Kiir had accused Machar of attempting a coup, which Machar has denied. More than 180,000 people have been displaced because of the fighting.
Fears of renewed fighting grew in the rebel-held cities of Bor, in Jonglei state, and Bentiu, in Unity state, the BBC said, because of a buildup of military personnel around both cities.
The BBC reported that mediators were preparing the groundwork for what they hoped would be direct talks later on Friday or Saturday.
Observers have said discussions likely would be difficult because two sides must agree on how to monitor a cease-fire. Also, Machar has refused to stop fighting before the talks and Kiir has ruled out any power-sharing arrangement.
The United Nations said it was flying more staff members into Juba to help in the aid effort and to protect civilians' human rights in South Sudan, which gained independence from Sudan in 2011.
The United States announced $49.8 million in additional humanitarian assistance to help victims of conflict in South Sudan.
"Even as we draw down our personnel, the United States remains deeply and actively committed to supporting regional and international efforts to end the violence in South Sudan, including the vital work of the U.N. Mission in South Sudan," the State Department said in its statement.
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