KHARTOUM - Relief agency World Vision has scaled back its operations in South Darfur after its staff suffered three attacks within a week, an agency official said on Thursday.

"World Vision has not suspended operations -- we have scaled down," Michael Arunga, communications manager for World Vision, told Reuters. "There have been three attacks in one week ... involving our staff."

The Christian agency has asked all non-essential staff in the south of the remote western Sudanese region to go on leave, with 77 of 308 Sudanese employees remaining and about half of its 20 international staff.

Since a Darfur peace deal was signed in May by only one rebel faction, insurgents have split into a dozen rival groups and formerly pro-government militias have turned on each other, creating a chaotic security environment. Seven thousand African Union peacekeepers have been unable to stem the violence.

Last week, a World Vision car was stolen by armed men in the northern part of the state. Later, three staff were shot and wounded, and their car was stolen.

In the latest incident, a driver was robbed at gunpoint of his vehicle just outside South Darfur's capital, Nyala. He was held for several hours, beaten and made to walk back to town.

Arunga said the agency was assessing security but did not want to suspend operations.

"If we are to pull out, that is going to be disastrous," he told Reuters by telephone from South Darfur. He said half a million people benefited from World Vision's activities in Darfur.

The world's largest aid operation helps more than 4 million people in Darfur, where conflict between mostly non-Arab rebels and the government is in its fifth year.

International experts estimate 200,000 people have been killed in the violence, described by Washington as genocide. The Sudanese government rejects the term and puts the death toll at 9,000.

The International Criminal Court has issued arrest warrants for a militia leader and a junior government minister accused of colluding in war crimes, but Khartoum refuses to hand them over.

Arunga said World Vision was continuing food distributions, as well as running health clinics and schools for children whose education had been disrupted by the conflict.

This week, British aid agency Oxfam said it would consider withdrawing from Darfur if security worsened. The Norwegian Refugee Council and Save the Children UK have already left.