The United Nations has suspended its humanitarian operations in Sudan's troubled South Darfur (search) area following a shooting that killed two aid workers, the agency said Monday.

The Sudanese employees of Save the Children (search) — medical assistant Abhakar el Tayeb and mechanic Yacoub Abdelnabi Ahmed — were killed Sunday when their convoy came under fire in South Darfur, said the U.N. statement.

It did not say who fired on the convoy.

Two main rebel groups are fighting government troops in Darfur in a bid for more power and resources. The U.N. describes the conflict as the world's worst humanitarian crisis, and international aid agencies have been struggling to feed and shelter almost 2 million people.

U.N. spokeswoman Radhia Achouri said the convoy was clearly marked as humanitarian.

"Our humanitarian operations in South Darfur are currently suspended whilst we review the situation. An African Union investigation is under way," the statement said.

Save the Children UK, which works closely with the United Nations (search) on humanitarian assistance in Darfur, operates a food center and medical clinics in the area.

"We deplore this brutal killing of humanitarian workers in Darfur. Our deepest sympathies are with the family and friends of our Sudanese colleagues," Ken Caldwell, director of International Operations for Save the Children, said in the statement.

In Brussels, Belgium, European Union Development and Humanitarian Aid Commissioner Louis Michel said Save the Children was doing "essential lifesaving work" in Darfur.

"This second fatal incident suffered by Save the Children in the past few months clearly shows the dangerous environment in which humanitarian organizations are working in this conflict," he said.

In October, two Save the Children employees were killed by a land mine in North Darfur.

Meanwhile, President Omar el-Bashir asked Parliament to renew Sudan's state of emergency for another year, citing security threats in Darfur, the official Sudan news agency reported.

El-Bashir said in a letter to Parliament that the situation in Darfur "necessitates precautionary measures to counter any development and to preserve the peace," Parliament speaker Ahmed Ibrahim El Tahir told SUNA.

The president first declared a state of emergency and dissolved Parliament in December 1999 in a bid to limit the power of a rival. The current state of emergency expires Jan. 1. The ruling party dominates Parliament and has never rejected a request submitted by the president.

In Abuja, Nigeria, on Monday, Sudanese government and rebel negotiators met for the first time for talks on ending the crisis. Later, however, the rebels announced a boycott of the talks, alleging a government offensive and saying a return to the negotiating table isn't possible until the government promises to cease attacks.

The African Union, which is mediating the talks, said they were confident talks could continue as planned Tuesday.

Earlier talks produced an accord on humanitarian access to the displaced and pledges to end hostilities — promises that were immediately violated.

The African Union said 13 violations of a cease-fire agreement were confirmed in September and 54 were documented between October and mid-December.

Disease and famine have killed 70,000 in Darfur since March, the World Health Organization says. There is no official reckoning of the overall toll of the war, which was sparked in 2003 when two non-Arab African rebel groups took up arms to fight for more power and resources.

The Sudanese government responded by backing an Arab militia known as the Janjaweed, which is accused of targeting civilians in a campaign of murder, rape and arson.