The spark that ignited the war occurred in Beirut on April 13, 1975, when gunmen killed four Phalangists (Kataeb) during an attempt on Pierre Jumayyil's life. Perhaps believing the assassins to have been Palestinian, the Phalangists retaliated later that day by attacking a bus carrying Palestinian passengers across a Christian neighborhood, killing about twenty-six of the occupants. The next day fighting erupted in earnest, with Phalangists pitted against Palestinian militiamen (thought by some observers to be from the Popular Front for the Liberation of Palestine).