A UN-African Union peacekeeper was shot and killed in Sudan's western Darfur region, a week after militiamen killed seven peacekeepers.
The Nigerian peacekeeper for the joint UN-AU Mission in Darfur (Unamid) was killed while on patrol in West Darfur, UN spokeswoman Marie Okabe told reporters in New York.
"This was a carjacking. He put up some resistance and got shot," Unamid's sector commander for West Darfur State, Balla Keita said.
Unamid's spokeswoman in Sudan, Shereen Zorba, condemned the attack, which she said occurred close to the Chadian border, and warned that the peacekeeping force was "stretched to the limit".
"It (the attack) is outrageous and despicable and the consequences are not in the best interests of Darfur," she said. "We call on the international community to act rapidly to strengthen the force. We need to be strengthened, otherwise we're sacrificing the lives of our men and women in vain."
Last week Unamid soldiers and police were ambushed on a routine patrol by about 40 vehicles full of armed militia in North Darfur. Seven were killed and over 20 more were wounded.
UN officials say UNAMID personnel are on high alert after Monday's request by the International Criminal Court chief prosecutor, Luis Moreno-Ocampo, that the court issue an arrest warrant for Sudanese President Omar Hassan al-Bashir on suspicion of masterminding genocide in Darfur.
Some 400 Irish Defence Forces personnel are serving in Chad, protecting up to 450,000 people in refugee camps who have fled the conflict in Darfur.
The UN has warned the peacekeeping force remains seriously undermanned - with only 9,000 out of a promised 26,000 soldiers - and poorly equipped. The force was sent to keep the peace in a remote region about the size of France.
Law and order has collapsed in Darfur, where international experts say five years of conflict has killed 200,000 and driven 2.5 million from their homes. Sudan puts the death count at 10,000 and accuses western media of exaggerating the conflict.