NEW YORK — The United Nations voted to extend the mandate of its peacekeeping operation in southern Lebanon for another year.

The U.N. Security Council voted unanimously Monday to keep the U.N. Interim Force in Lebanon on patrol in southern Lebanon on the border with Israel until Aug. 31, 2011.

The Council based its decision on what it considers the unstable situation on the border between Lebanon and Israel.

UNIFIL has been deployed in southern Lebanon since 1978. Its mandate was strengthened in 2006 following the Second Lebanon War to monitor the U.N.-brokered cease-fire. Nearly 12,000 UNIFIL personnel are serving in the area.

On Aug. 3, Israeli and Lebanese troops fired at each other after Israel began trimming a tree on its side of the Blue Line, which demarcates the border between the two countries. An Israeli soldier was killed and one was injured in the shooting. Three Lebanese soldiers and a journalist were killed.