The 1982 Lebanon war began on 6 June 1982, when Israel invaded again for the purpose of attacking the Palestine Liberation Organization. The Israeli army laid siege to Beirut. During the conflict, according to Lebanese sources, between 15,000 and 20,000 people were killed, mostly civilians. According to American military analyst Richard Gabriel, between 5,000 and 8,000 civilians were killed. Fighting also occurred between Israel and Syria. The United States, fearing a widening conflict and the prestige the siege was giving PLO leader Yasser Arafat, got all sides to agree to a cease-fire and terms for the PLO's withdrawal on 12 August. The Multinational Force in Lebanon arrived to keep the peace and ensure PLO withdrawal. The PLO leadership retreated from Beirut on 30 August 1982 and moved to Tunisia.