The United Nations reports a halt to international aid work in the displaced persons' camps of Zalinge, in Sudan's Darfur region.

The U.N. refugee agency says international groups suspended their activities in the camps after a mob killed three water workers on Thursday. It was unclear what caused the violence.

Friday, spokesman Ron Redmond said agency is "extremely concerned" about what he called the continued deterioration in Darfur's security situation. Redmond listed a number of attacks on relief groups over the past week, including one where an aid worker was shot dead in North Darfur.

World leaders have been pressing Sudan to accept a U.N. peacekeeping force in Darfur. The government is still rejecting any U.N. deployment to the region, where more than three years of violence has killed nearly 200,000 people, and displaced some two million others.