"Since Israel's withdrawal from southern Lebanon in May 2000, there have been hundreds of violations of the "blue line" between the two countries. The United Nations Interim Force in Lebanon (Unifil) reports that Israeli aircraft crossed the line "on an almost daily basis" between 2001 and 2003, and "persistently" until 2006. These incursions "caused great concern to the civilian population, particularly low-altitude flights that break the sound barrier over populated areas". On some occasions, Hizbullah tried to shoot them down with anti-aircraft guns.In October 2000, the Israel Defence Forces shot at unarmed Palestinian demonstrators on the border, killing three and wounding 20."