UN aid agencies have appealed to the warring parties to end the violence in Darfur, saying otherwise the aid keeping millions alive will be "irreversibly jeopardised".

The statement issued jointly by 14 agencies said an influx of foreign aid was the only thing "holding the line" for 2.5 million refugees and over 1 million civilians in Darfur.

The humanitarian groups say they were pushed to issue the new appeal by the increased targeting of aid workers in the region, the splintering of rebel groups into lawless factions without clear leadership and government restrictions, making it ever more difficult for aid workers to operate.

'Humanitarian space'

Ted Chaiban, the Sudan country manager for the UN Children's Fund, said: "The humanitarian space that we operate in is shrinking."

With repeated military attacks and shifting front lines, December was the worst month in Darfur in over two years, the UN agency statement said.

It followed six months of escalating violence, during which 30 UN and aid compounds were directly attacked, forcing about 400 UN and aid workers to leave the region.

During the same period, 12 aid workers were killed in zones controlled by rebels and government forces.

Alun McDonald, the spokesman for the British aid group Oxfam in Sudan, said: "Before, aid workers were being caught up in the violence, now they're actually being targeted.

"It's not the occasional vehicle getting lost, it's compounds being looted in coordinated attacks."

'Trying to understand'

UN and other humanitarian groups say the turning point came on December 18, when at least four different aid organisations were attacked in the South Darfur camp of Gereida, the regions largest with 130,000 refugees.

Offices and housing compounds were simultaneously raided, cars and radio equipment plundered, and some aid workers endured mock executions while the unidentified assailants raped a female aid worker from the French aid group Action Contre la Faim.

Philippe Conraud, ACF's Sudan coordinator, said: "We're still trying to understand what happened.

"The fact that we can't assess why this took place is worrying us for the future."

Nearly all aid workers have evacuated Gereida, a zone reputed to be controlled by fighters from the faction of the Sudan Liberation Movement led by Minni Minawi, the one rebel leader who signed a peace agreement with the government last May.

Aid workers had initially thought the attacks might have been carried out by a rebel squad seeking equipment so that it could break from Minawi and resume fighting, but now say they have no idea who was responsible.

'Little explanation'

Conraud said Minawi had provided him with "very little explanation", but had promised to fully investigate the incident.

Aid groups and UN officials have for months been alarmed by the rapidly deteriorating conditions faced by civilians in Darfur, where over 200,000 people have been killed since rebels took up arms against the central Sudanese government in 2003, accusing it of neglect.

The government is accused of retaliating against civilians with air raids and by unleashing the janjaweed, militias of Arab nomads blamed for the worst atrocities in the conflict.

The statement said: "Villages have been burnt, looted and arbitrarily bombed and crops and livestock destroyed. Sexual violence against women is occurring at alarming rates. This situation is unacceptable."

PHOTO CAPTION

A rebel with the National Redemption Front at an outpost in Umm Sidir, North Darfur, August 28, 2006. (Reuters)