A top militant with ties to Hamas was killed by a car bomb Friday, and his followers blamed security forces loyal to Palestinian President Mahmoud Abbas' Fatah movement for the assassination.

A shootout at the militant's funeral killed three more people and wounded more than 20, raising the possibility of a wider Hamas-Fatah clash just two days after Hamas assumed power, replacing Fatah at the helm of the Palestinian Authority.

The militant, Abu Yousef Abu Quka, was a senior commander of the Popular Resistance Committees, an umbrella group of about 200 gunmen. About half the gunmen are allied with Hamas, including Abu Quka, and the other half with Fatah. Abu Quka's supporters blamed the Fatah-dominated Preventive Security Services for his assassination.

Hamas has pledged to restore order in the lawless Gaza Strip and West Bank. However, Palestinian security forces, most of them affiliated with Fatah, are involved in the violence, and Hamas has little control over them.

Late Thursday, an offshoot of Fatah carried out its first suicide bombing against Israel since a February 2005 truce, killing four Israelis in the West Bank. Abbas, a moderate who wants to restart peace talks with Israel, denounced the attack. "We as the Palestinian Authority do not accept it," he said.

Abu Quka was killed Friday when his white Subaru blew up in a Gaza City street. The PRC initially blamed Israel, which denied involvement, and then pointed to the Preventive Security Service. "There is a long history of conflict between us," said PRC spokesman Abu Abir, an Abu Quka ally. "The Preventive Security always tries to demean our members."

Abu Abir said that gunmen loyal Mohammed Dahlan, the powerful former Prevent Security Service chief in Gaza and a Fatah lawmaker in the new Palestinian parliament, were caught spying on Abu Quka's home Thursday. Abu Quka said he and his allies would not wage "an open war" on Dahlan and several other top security commanders.

Palestinian intelligence officials said Abu Quka was a known Hamas supporter, and appeared to have been targeted for his loyalties. The officials, fearing for their safety, spoke on condition of anonymity.

Dahlan, who was traveling in the United Arab Emirates, dismissed the PRC's allegations as "baseless ugly accusations."

When Abu Abir called a news conference to discuss the killing, rival gunmen burst on the scene, sparking a shootout. Hospital officials said two boys, ages 15 and 13, were wounded, one seriously.

Dozens of gunmen gathered outside the hospital where Abu Quka's body was taken, crying, screaming and firing into the air. Accompanying the body, hundreds of gunmen marched through the streets of Gaza City.

With tensions heightened, gunfire broke out at the funeral. Hospital officials said three people were killed, including two bystanders and a PRC member who had joined the procession. Twenty-five others were wounded.

Hamas' new interior minister, Said Siyam, who is now in charge of several security agencies, including preventive security, pledged to bring Abu Quka's killers to justice and called for national unity. "We regret the exchange of accusations and mentioning of names," he said.

After the funeral, dozens of Fatah-linked gunmen blocked the roads leading to Samir Masharawi, another strongman close to Dahlan. A spokesman for the gunmen pledged to take "all necessary measures against Abu Abir. He must be punished."

Friday's unrest came hours after Fatah-linked militants carried out a suicide bombing in the West Bank. The attack was carried out by a militant who disguised himself as a Jewish hitchhiker and then killed himself and four people in a car that picked him up.

Israeli security officials say they expect more suicide bombings from Fatah militants now that Hamas has taken power.

With Israel's acting Prime Minister Ehud Olmert planning to pull out of much of the West Bank in the coming years, Fatah-linked militants might try to step up violence to create the impression Israel is retreating under fire.

Hamas has claimed that its years of attacks pushed Israel out of the Gaza Strip last year.

Alternatively, security officials said, Fatah militants might want to turn up the heat on Hamas, which is under heavy international pressure to renounce violence.

Israeli officials said the suicide bomber had been released from a Palestinian jail recently.