Most of those newly displaced had fled fighting around Golo and Daya in the Jebel Marra area of West Darfur, said Andy Pendleton, the area coordinator for the UN Office for the Coordination of Humanitarian Affairs (OCHA).

The exact number of those displaced could not be immediately established.

The situation in Golo and Daya remained "very tense". Humanitarian agencies have been reducing their staff in West Darfur State in the past month due to rising tensions in the area, Pendleton added.

Other sources said the latest fighting in West Darfur had been going on for about five days and involved Sudanese government troops and rebels of the Sudanese Liberation Army.

Dawn Blalock, spokeswoman for OCHA in Sudan, said some 400 internally displaced persons in Sharia, South Darfur, had been harassed by militiamen on horseback. Most of them were women and children.

"OCHA has been in touch with the appropriate officials asking them to intervene in the area," she said by telephone from the Sudanese capital, Khartoum.

By Friday, at least 90 humanitarian staff working for several international nongovernmental organisations had been evacuated from Golo and Daya.

The UN Mission in Sudan said it evacuated seven of its staff from Sharia to Nyala, the capital of South Darfur, on Thursday.

Tension in the region, Pendleton said, had also been fuelled by a standoff between Sudan and Chad. The two neighbours have traded accusations for months, each side claiming the other supports its insurgents.

In December, the Chadian government declared "a state of belligerence" between itself and Sudan following a deadly border attack Chad blamed on the Sudanese government.

The Darfur conflict erupted in early 2003 when rebels took up arms against Khartoum to end what they called the neglect and oppression of the mainly black inhabitants of Darfur, a semi-desert region the size of France.

The Sudanese government responded by backing Arab militias known as the Janjawid, who have been widely accused of committing atrocities against civilians.

Some 3.4 million people continue to be affected by the conflict, according to the UN, of whom 1.8 million are internally displaced and 200,000 have fled to neighbouring Chad.