After continued PLO-Israeli exchanges, Israel invaded Lebanon on June 6 in Operation Peace for Galilee. By June 15, Israeli units were entrenched outside Beirut and Yassir Arafat attempted through negotiations to evacuate the PLO. It is estimated that during the entire campaign, approximately 20,000 were killed on all sides, including many civilians. A multinational force composed of U.S. Marines and French and Italian units arrived to ensure the departure of the PLO and protect civilians. Nearly 15,000 Palestinian militants were evacuated by September 1.