Palestinian guerrilla groups, such as the Syrian-backed Al Saiqu, the marxist-oriented Popular Front for the Liberation of Palestine (PFLP), and Al Fatah, headed by Yasir Arafat (1929-), engaged in guerrilla raids against Israel, their enemy, as a means of keeping it on the defensive. Under the theoretical leadership of Arafat, who founded the Palestine Liberation Organization (PLO) in 1964 and became its leader in 1968, the raids were orchestrated before and between major Arab-Israeli wars. The guerrillas bombed Israeli schools, buses, and marketplaces' conducted random assassinations; and fired rockets at civilian centers. Before 1967, these terrorist raids came chiefly from Syria; after the Six Day War (1967) the guerrillas were based in Jordan until they were forced into Lebanon during the Jordanian Civil War of 1970-71. Arafat's Palestinians were forced out of Lebanon in 1983. Palestinian raids eventually became more infrequent, being replaced by imitative raids from Shi-ite groups. Two of the Palestinian attacks received worldwide condemnation: their "Black September" (September 6-9, 1970) hijacking of commercial jetliners (which forced 435 passengers to become hostages in Amman) and the 1972 raid at the Munich Olympic Games, during which 11 Israeli athletes were killed. In late 1987, Palestinians in Gaza rioted against Israeli police, resulting in further violence in other Israeli-occupied territories. The PLO consequently proclaimed an independent state in 1988, nominally recognized Israel, and gained minor diplomatic contact with the US. In uprisings termed "intifadeh," Palestinians opposed Israeli troops in the West Bank and Gaza in 18989 and 1990; scores of Palestinians were injured or killed. Negotiations between the PLO and Israel led to historic agreements in September 1993: Israel accepted the PLO as the Palestinians' representative, the PLO granted Israel's right to exist, and the Palestinians gained limited self-rule in the West Bank and Gaza (officially signed in 1994 and augmented in 1995). Palestinian anger and despair over paralysis in the peace process, brought on by the election in May 1996 of Israel's hard-line prime minister Benjamin Netanyahu (1949-), helped lead to furious confrontations between armed Israelis and Palestinians in late September 1996, after the opening of the ancient Hasmonean tunnel, dug by Israelis in Arab East Jerusalem (proposed capital of a future Palestinian state). The US tried to find diplomatic ways to restart the peace process, and in early 1997 Israel agreed to a partial withdrawal from the West Bank city of Hebron. Extremists on both sides continued to clash on the roads and in Jerusalem, various Jewish settlements, and some religious sites. Israeli-Palestinian coexistence remained tenuous despite new Israeli-Palestinian peace talks and accords at Wye River, Maryland, mediated by the US (mid-October 1998); Israel agreed to concede territory in return for strengthened security.