In this photo released by the United Nations Mission in Sudan (UNMIS), a Zambian U.N. peacekeeping soldier sits atop an armored personel carrier as he patrols the area in the contested border town of Abyei, Sudan, Monday, May 30, 2011. The northern Sudanese government has called for Southern Sudan's troops stationed in northern border states to withdraw within two days. But the south has warned that it will not withdraw its forces because the soldiers are local men. The standoff follows the north's occupation of the disputed border region of Abyei last week. (AP Photo/UNMIS, Stuart Price) EDITORIAL USE ONLY, NO SALES