An interesting history of the PLO vs Other Arab States:

Black September

The day after the destruction of the hijacked planes [hijacked September 6, 1970] King Hussein declared martial law, dismissed Rifai’, recalled Field Marshal Habis Al Majali to active duty and appointed him commander in chief, and entrusted the formation of a military government to the Palestinian born General Mohammed Daoud. Arafat stormed around Amman making statements but there were no last minute moves to salvage the situation, even after the Arab governments showed little inclination to stand in Hussein’s way.

The fighting began the following day, with a Jordanian artillery barrage against the PLO stronghold of Zarqa. Within hours similar attacks were being directed against several areas of Amman, including the strategic Jabal Al Hussein, and on refugee camps such as Al Wahdat which had raised the flag of the Republic of Palestine. For the first time Arafat used the word ‘genocide’ to describe what was happening to the Palestinians...

Note that Israelis are not carrying out this "genocide," but other Arab nations. The actual number of Palestinians is subject to much debate, but the accepted minimum is 2,000. There's also this account:

Jordan PLO Syria Black September 1970-1971

The 1967 defeat radicalized the Palestinians, who had looked to the Arab countries to defeat first the Yishuv (the Jewish community of Palestine before 1948), and after 1948 the State of Israel, so that they could regain their homeland. The PLO had no role in the June 1967 War. After the succession of Arab failures in conventional warfare against Israel, however, the Palestinians decided to adopt guerrilla warfare tactics as the most effective method of attacking and defeating Israel. In February 1969, Arafat (who remained the leader of Al Fatah) became head of the PLO. By early 1970, at least seven guerrilla organizations were identified in Jordan. One of the most important organizations was the Popular Front for the Liberation of Palestine (PFLP) led by George Habash. Although the PLO sought to integrate these various groups and announced from time to time that this process had occurred, they were never effectively united....