Rebel soldiers and government troops in South Sudan are fighting for control of Malakal, the capital of oil-producing Upper Nile State.
Clashes in the town began Tuesday and picked up again Wednesday, with government officials acknowledging the army is not in full control of the town.
Late Tuesday, the U.N. Security Council voted to to send an additional 5,500 peacekepeers to troubled South Sudan, where U.N. official Toby Lanzer said it is likely thousands of people have been killed in fighting over the past 10 days.
Witnesses say many people have been targeted for being ethnic Dinka or Nuer. In a Christmas Eve message, President Salva Kiir called on South Sudanese to stop all tribal violence.
Meanwhile, the U.N. mission in South Sudan is denying a report that a mass grave was found in Bentiu, the Unity State capital held by rebels.
The U.N. human rights office said Tuesday that the bodies of up to 75 ethnic Dinka soldiers had been found. But the U.N mission says the report was an "inflation" of a skirmish that resulted in about 15 fatalities.