Khartoum, Sudan ? Gunmen ambushed troops of the joint United Nations-African Union peacekeeping force in Sudan’s Darfur region Monday night, wounding four soldiers, a spokesman for the mission said.

The attack was the first reported violence against peacekeepers since the International Criminal Court issued an arrest warrant last week for Sudan’s president, accusing him of war crimes in the western region.

The peacekeepers were returning to base in el-Geneina, the capital of West Darfur, when they were attacked, said Noureddine Mezni, spokesman for the U.N.-AU mission. One soldier was in serious condition and all the wounded were being evacuated to the mission’s headquarters in northern Darfur, he said. He could not provide further details.