The United Nations expressed concern over the safety of Darfuri civilians who had sought refuge in the rebel-held area near the Chad border after the government took back three major towns near the state capital el-Geneina on February 8 and following reports of bombing on Monday.

"From the morning there are clashes and they are still going on," said Sheikh el-Din Mahin, a Darfur rebel Justice and Equality Movement (JEM) official in the area.

"There are planes bombing -- helicopters and Antonovs," he added.

A Reuters witness saw army helicopters taking off and landing at el-Geneina airport. Sudan's army spokesman said the army had begun a "cleansing" operation of the whole area.

"There are elements of Chadian opposition and Chadian government elements supporting Darfur rebels in the area who are attacking civilians," the spokesman told Reuters.

Chad and Sudan accuse each other of supporting insurgents in Darfur and neighbouring eastern Chad. President Idriss Deby fended off a rebel assault on N'Djamena earlier this month, which he accused Khartoum of organising.

The U.N. refugee agency (UNHCR) said it was temporarily evacuating six or seven staff from the Chad side of the border where between 7,000-12,000 Darfur refugees had gathered since the February 8 offensive.

BOMBING

"We have no confirmation or further details of the alleged bombing raid but bombing could be heard from Birak," UNHCR spokeswoman Jennifer Pagonis said in Geneva of the area in eastern Chad.

She said refugees had arrived carrying a woman who lost both legs in the bombing of Aru Shurow camp near Jabel Moun a day earlier. The woman later died.

U.N. humanitarian chief John Holmes said he was worried about thousands of civilians seeking refuge inside Jabel Moun following the bombing of the mostly empty Aru Shurow camp.

"I am very concerned for the civilian population caught in the middle of this violence. Should further attacks occur, the consequences for 20,000 civilians in this area could be disastrous," he said in a statement.

He said a total of 160,000 civilians in the area could face severe consequences from the violence.

Residents said government-allied militia and bombing raids had killed 114 people in the February 8 offensive. The army denies any link to the militia and says many of those killed were rebels in civilian clothes.

A Reuters witness has seen many armed men on horses and camels wearing military uniforms north of el-Geneina. A Sudanese tank with the word "death" written on the back was also seen on the road north.

Mostly non-Arab rebels took up arms in Darfur in early 2003 accusing central government of neglect of the region. International experts estimate 200,000 have died and 2.5 million have been driven from their homes in the rape, looting and murder that followed.

A joint U.N.-African Union mission took over peacekeeping duties on December 31 but with only 9,000 of the required 26,000 troops and police on the ground it has not yet been able to do its job properly.