RAMALLAH, West Bank ? Masked Palestinian gunmen burst into a meeting of the ruling Fatah Party on Thursday, shooting into the air and forcing participants to disperse in a brazen challenge to Palestinian leader Mahmoud Abbas.

The incident cast doubt on his authority as he comes under increasing pressure from Israel to disarm militants.

Despite the unrest, Abbas said Thursday that he was confident militants would agree to a formal cease-fire at a meeting next week in Egypt.

Abbas and Israeli Prime Minister Ariel Sharon declared an end to more than four years of bloodshed at a summit in Egypt a month ago, but Abbas has yet to get the violent Hamas and Islamic Jihad to formally join the truce.

Events Thursday in Ramallah showed Abbas faces problems just as serious in his own Fatah Party, as younger, militant cadres continue to demand a piece of the leadership pie.

More than 1,000 Fatah grass-roots activists were meeting in the West Bank city of Ramallah when two dozen gunmen dressed in military-style fatigues, their faces covered, burst into the room in a shiny new hotel where the session was in progress.

The gunmen — from the Al Aqsa Martyrs Brigades, a violent group affiliated with Fatah — rampaged through the room and shouted slogans charging the Fatah leadership with complicity in widespread corruption.

Shocked participants ducked and scrambled for the exits as the intruders, brandishing assault rifles, began throwing chairs around, ordering everyone to leave.

The meeting broke up in disarray, and as the Fatah members fled, the gunmen fired in the air outside the hall for several minutes. No one was hurt, but the gunmen made their point — the session did not reconvene.

“Our demands are for change and reform,” said Menwer al-Aqraa, an Al Aqsa commander in Ramallah, without elaborating. He said, however, that his group would not disarm, though it remains loyal to the Palestinian Authority.