On the 4 June 1982, Israel launched a bombing campaign by air and sea against Lebanon, followed the next day by a full-scale land invasion. The Israeli Army occupied the south of Lebanon, causing vast destruction and thousands of casualties; 15.000 persons were killed, half under the age of 13.
Initially with the declared intention of driving Palestinians out of a zone 25 miles wide that bordered on Israel, the Israel Army then moved its troops to Lebanon’s capital Beirut and put the entire city under siege. Its goal turned to “to eliminate the PLO”, which was located in Beirut. The Palestinian resistance and National Lebanese government confronted the aggression and prevented Israeli soldiers from entering the city of Beirut for 78 days.
The PLO’s withdrawal from Beirut came only after a cease-fire had been arranged with the United Nations, which was to be maintained with the help of multinational troops. PLO troops withdrew from Beirut and were transferred to neighbouring countries.
Despite the cease-fire agreement and the withdrawal of PLO troops, Israeli forces advanced into West Beirut. On 16 September 1982, the Israeli Army gained control of most of West Beirut and took up positions around the Palestinian refugee camps. The following day, the Security Council unanimously adopted resolution 520 condemning the recent incursions by Israel into Beirut in violation of the cease-fire agreements and of Security Council resolutions.
The US envoy requested Israel to guarantee the safety of Palestinian refugees in Lebanon upon the withdrawal of PLO troops. Instead, on 16 and 17 September 1982, Israeli forces allowed Lebanese Phalangist units, known to be an Israeli ally, to enter the Sabra and Shatila Palestinian refugee camps in West Beirut. Under Israeli surveillance, the Phalangists committed a horrific massacre in the camps killing over 800 people, including women and children.