Citing increased threats to safety and security, U.N. officials announced that most of its civilian international and national staff has been evacuated from the Sudanese town. Abyei is located in the oil-rich region of the country which is facing an increased level of rebel attacks and military responses from the government, the United Nations said.

Only the head of the U.N. office and a few others remain in the almost deserted town. Officials say they are still receiving reports of gunfire in the region between government forces and the rebel Sudan People's Liberation Army.

"An impasse over the boundaries of Abyei has been one of the main stumbling blocks hindering the full implementation of the comprehensive peace agreement, which ended more than two decades of north-south conflict in Sudan," the release said.