UN Secretary-General Ban Ki-moon on Wednesday strongly condemned the commandeering of humanitarian vehicles and the theft of food and other desperately needed aid by government and anti-government forces in violence-torn South Sudan.

The UN chief expressed alarm at the rising number of deaths in the fighting in the world's newest nation, spokesman Martin Nesirky said.

Fighting between loyalist troops and renegade forces in oil-rich South Sudan since mid-December, largely along ethnic lines, has left nearly 10,000 people dead, according to one estimate by an International Crisis Group analyst.

The secretary-general singled out the reported deaths of 200 civilians fleeing violence in Malakal in Upper Nile state who drowned when their boat sank in the Nile on Saturday.

Nesirky said the UN mission reported Wednesday that fighting has stopped in Malakal but sporadic gunfire can be heard some distance from the UN peacekeeping base there, where some 20,000 civilians are being protected.

Nesirky said a teen who sought shelter at the base in Malakal was killed by gunfire that entered the compound Tuesday, and dozens of civilians and a UN military officer were wounded.

Doctors Without Borders, the medical humanitarian organization, said Wednesday its teams in Malakal and Nasir in Upper Nile have treated 116 people who suffered gunshot wounds, a sign of how intense the latest fighting has been.

The UN chief also expressed concern at the rising number of people displaced by the fighting, which surpassed 400,000 this weekNesirky said.

Ban called on all parties to stop the violence and engage in peace negotiations in Addis Ababa, Ethiopia, led by a bloc of East African countries known as IGAD, the spokesman said.

In Addis Ababa, a signing ceremony between the two sides had been expected Wednesday evening, but it was postponed.

Deputy Secretary-General Jan Eliasson told a UN meeting on genocide prevention that the UN decision to open its peacekeeping bases in South Sudan, where some 65,000 people have sought refuge, has saved thousands of lives.