Tens of thousands of Fatah supporters packed Gaza's main soccer stadium Sunday in a show of strength to boost the movement in its increasingly violent struggle against the Islamic militant group Hamas.

The demonstration came as masked Fatah gunmen released a video of a kidnapped Hamas official, threatening to expand attacks against Hamas if it rejects calls to disband its militia in the Gaza Strip. The video, reminiscent of scenes in Iraq, marked a new tactic in the latest spate of Palestinian factional violence.

Fatah's strongman in Gaza, Mohammed Dahlan, was given a hero's welcome as he entered the stadium. As he began speaking, he shooed away the guards protecting him. "Let Hamas shoot me," he said as the crowd erupted in applause. Fatah gunmen fired in the air during his speech.

The stadium demonstration marked the 42nd anniversary of the founding of Fatah by the late Yasser Arafat, but was meant to send a clear message to Hamas, which has defiantly rejected Fatah's calls to outlaw the Gaza militia.

Fatah and Hamas have been locked in a bloody struggle for control of the Palestinian government since the Islamic group won parliamentary elections last year. The victory ended four decades of Fatah political domination, though the group still controls the powerful Palestinian presidency.

Sunday's gathering was the largest Fatah demonstration in Gaza since 1994, and a sea of yellow Fatah flags fluttered in the wind. Roads in southern Gaza were packed with motorists trying to reach the stadium.

In his fiery speech, Dahlan called Hamas' deadly assault on the home of a Fatah security commander last week a "turning point."

"If they think the murderers will not be punished, they are mistaken," said Dahlan. "If they attacked one Fatah person, we'll attack two more."

Hamas lawmaker Salah Bardawil called Dahlan's speech "defamation" that served the interests of Israel. He said Hamas knew Fatah was well armed, but hoped the weapons would be used "against the occupation (Israel) and not against Hamas."

More than 30 Palestinians have been killed in factional violence since early December. The fighting has been mostly limited to the Gaza Strip, where Hamas has its power base, but it has begun to spread to the West Bank, where Fatah is much stronger.

Tensions heightened Saturday after President Mahmoud Abbas of Fatah outlawed Hamas' so-called Executive Force, its main military unit in Gaza. Hamas responded by saying it would double the size of the force to 12,000 fighters and resist any attempts to disarm it.

In the video, Mahdi al-Khamdali, the deputy mayor of Nablus and a Hamas official, standing in a jacket and tie, was surrounded by masked militants in army jackets.

One of the men read a statement from a folded sheet of paper, identifying the gunmen as Fatah members. He mentioned the Hamas force and threatens new attacks against Hamas, but stops short of threatening to kill the politician.

"From this date we announce loudly that we are not going to keep silent in the West Bank about the crimes of this criminal force," one of the militants said in the video. "If any crime takes place against one of our people in Gaza, there will be an operation in the West Bank and we will not exclude anybody from this decision."

In Gaza City, six pro-Hamas militant groups voiced their support for the Executive Force. "We are not going to allow anyone to assault or attack or harm any member of the Executive unit," Abu Abir, spokesman for the Popular Resistance Committees, told a news conference. "We are going to deal with them in the same manner that we deal with the occupation and its collaborators."

Nablus was the scene of a large Israeli operation Sunday. Troops entered the city before dawn, surrounded a building and detained six people, the army said.

The army said the operation had thwarted a planned suicide bombing and that two of those arrested were masterminds of the attack. Troops also found two explosives belts, the army said. According to military officials, the would-be bomber, a 16-year-old Palestinian boy, had been arrested previously.