Fatah enjoys Western support and has been pressured not to forge a unity agreement with the militant Hamas, facing a potential cutback in foreign aid if it does.
Friday's rally also served as a reminder of the conflicts within Fatah itself that continue to dog the movement: Officials cancelled the event halfway through after 20 people were injured due to overcrowding, and shoving matches erupted between separate Fatah factions.
Yahiya Rabah, a top Fatah official in Gaza, said the rally was cancelled "due to the huge number of participants and logistical failures."
But witnesses said one pushing match was between supporters of Abbas and partisans of Fatah's former Gaza security commander Mohammed Dahlan, who was expelled from the party because of conflicts with Abbas.
Another Fatah official, who spoke anonymously because he did not want to embarrass the party, said the rally was cancelled because hundreds of Dahlan supporters jumped up on the stage and clashed with Abbas supporters.
Fatah spokesman Fayez Abu Etta attributed the injuries to overcrowding and the excitement of the rally. Later, more Palestinians were injured when part of a stage collapsed. Youths also clashed and stabbings were reported. Gaza health official Ashraf al-Kidra said overall 55 people were injured, including three critically.
There was one death during the rally: A 23-year-old Fatah activist was electrocuted while trying to hang a flag on an electric pole.
Overnight, throngs had camped out in a downtown Gaza square to ensure themselves a spot for the anniversary commemoration of Fatah's 1965 founding, and tens of thousands marched early Friday carrying Fatah banners. When the rally began, people stampeded to the stage to try to shake leaders' hands.
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