By Alan Johnston
BBC News, Gaza
The Palestinian faction Fatah has staged a large and highly-charged political rally in Gaza.
Gaza City's main stadium was filled by Fatah supporters
The event, the largest of its kind for years, came at a time of extreme tension between Fatah and its rival, the Hamas movement.
About 30 people have been killed in clashes over the past month.
Many thousands of Fatah's followers filled Gaza City's main stadium, and gave a hero's welcome to Fatah's strongman in Gaza, Mohammed Dahlan.
He focused his anger on an armed Hamas unit called the "executive force".
In a particularly violent episode a few days ago, it stormed the home of a very senior Fatah security man and killed him and his bodyguards.
Mr Dahlan told the crowd that this had been a turning point. He called the members of the Hamas force murderers and said that they would not go unpunished.
On Saturday, the Fatah-controlled presidency declared the executive force to be illegal, but Hamas has rejected the charge and responded by announcing plans to strengthen the unit.
And in an obvious reference to Fatah, a senior Hamas militant has said that blame for the bloodshed in Gaza lies at the door of, as he put it, those who have received weapons from America.
The US is keen to bolster the more moderate Fatah faction, and there have been recent reports of American involvement in the shipping of guns to the Fatah-controlled security forces.