Hamas security forces fanned out across a tense Gaza Strip Sunday, following a mysterious weekend car bombing that killed six people and sparked the toughest Hamas crackdown against its Fatah rivals in months.

Human rights groups said Hamas released over a dozen of the some 200 Fatah men it arrested Saturday in connection with the bombing, which killed five Hamas men and a 4-year-old girl. But Hamas police remained deployed in force around Gaza City, manning roadblocks and checking cars.

Meanwhile Palestinian security forces loyal to Abbas detained more than 30 Hamas activists, including two officials, in the West Bank cities of Tul Karm and Jenin on Sunday, Palestinian security officials said. They gave no reason for the arrests.

The Hamas government said Saturday following an emergency government meeting that the "revolutionary stream" - as former Gaza Fatah leader Mohammed Dahlan's supporters are called - were responsible for the beachside blast late Friday.

The explosion occurred at about 8:30 P.M. near the Khalil cafe, a known meeting place for Hamas men. It was followed by the toughest crackdown against Fatah in recent months.

Meanwhile, on Sunday, Hamas security forces clashed with gunmen from the Army of Islam, an al Qaeda-inspired group, in the Gaza Strip.

One Hamas commander was seriously wounded and a militiaman killed in the fighting, which started when the Hamas forces sought to arrest some Army of Islam gunmen, Hamas officials and local residents said. Two Army of Islam gunmen were arrested.

The Army of Islam is not allied with Fatah, but is heavily armed and is seen by Hamas as a threat to the public stability it has largely managed to enforce since taking control of Gaza a year ago.

Hamas launched a crackdown on militant groups over the weekend after the series of beachside bombings.

As part of the crackdown, Hamas has arrested more some 200 activists from Fatah, the secular faction of Western-backed Palestinian President Mahmoud Abbas. Islam Shahwan, a Hamas police spokesman, said his men seized huge amounts of explosives and weapons from Fatah in Saturday's operations.

Abbas urges immediate Palestinian reconciliation talks

Meanwhile, Egyptian President Hosni Mubarak hosted Abbas on Sunday for talks on a number of regional issues. Abbassaid following the talks on Sunday that Egypt plans to relaunch immediate reconciliation talks between his Fatah faction and the militant Hamas group which controls Gaza.

The Palestinian president said he has preconditions for the dialogue. Abbas' willingness to enter new talks with Hamas comes after he vowed for more than a year not to talk with the Islamic movement unless it first gives up control of the Gaza Strip.

Abbas said Egypt would call representatives of Palestinian factions "within days" for dialogue sessions in Cairo. Mistrust and disputes over conditions and terms for a dialogue had buried several dialogue calls in the past year.

Hamas official Sami Abu Zuhri said Abbas's call for dialogue with Hamas was "not honest," saying investigations into Friday's killings showed some senior Fatah officials were involved.

"The bombing and killings in Gaza proved that Fatah was not interested in dialogue with Hamas, and all they aspired [to] was to cause anarchy and chaos," the Hamas spokesman said.

Hamas has always rejected Abbas's demand that it relinquish control of Gaza, which it seized last year after routing the Western-backed Palestinian leader's security forces following a brief civil war that left dozens of people dead.

Abbas denied Hamas suggestions he was under U.S. pressure not to restore dialogue with the Islamist group, saying "if something like that happened we would reject it."

Gaza blast

The dead in Friday's explosions were named as Sarin a-Safadi, the 4-year-old; Nihad Masbakh, considered the head of the military wing of Hamas in the Shajaiyeh district of Gaza City; Iyad al-Hayeh, a nephew of one of Hamas' leaders in Gaza, Khalil al-Hayeh (whose son was also seriously injured in the blast); Nidal al-Mbayid and Osama al-Khalu. The identity of the fifth Hamas man is unknown.

More than 20 Palestinians were injured, mostly passers-by.

The explosive charge was set off under a car belonging to one of the Hamas men, which was parked outside the coffee shop.

Sources in Hamas said the Palestinian Authority television in Ramallah broadcast pictures of the car hit in the Gaza blast accompanied by joyful music.

Hamas leader Ismail Haniyeh convened an emergency government meeting on Saturday, after which he issued a statement blaming Fatah for the bombing. The statement called on the Gaza authorities to find the people involved in "the horrible crime yesterday."

"Those guilty will be subject to justice in order to be an example for anyone who might think to shed the Palestinian blood," the statement read. If convicted, the perpetrators could face the death penalty.

Earlier Saturday, Hamas security forces arrested dozens of Fatah supporters, hurled grenades at the home of one Fatah leader and set up checkpoints across Gaza in a crackdown on the rival faction.

A Gaza-based human rights group reported Hamas security officials arrested at least 160 Fatah loyalists, and some 40 institutions connected to the group were raided. Fatah leaders said more than 200 of its people were rounded up, including its top leader in Gaza, Ahmad Nasser.

Fatah leaders denied involvement in the explosion, and an aide to Palestinian President Mahmoud Abbas said the consequent crackdown was reducing prospects for eventual reconciliation between the rival groups.

If Hamas was in fact targeted, it would be the deadliest such attack since the Islamic militants ousted Fatah-allied security forces from Gaza in a violent takeover more than a year ago.

Earlier Saturday, Thousands of Hamas loyalists marched in the funeral of the explosion's victims, waving their movement's green flag. Gunmen fired automatic rifles into the air and angrily vowed revenge.

"The collaborators who did this must be hung in Palestine Square and shot," al-Hayeh, the lawmaker, said in a eulogy, referring to Gaza City's main square.

"The people who stand behind this (attack) are from Fatah," al-Hayeh said. "We hold their leaders responsible ... and say, either be nationalists or collaborators, the choice is yours," he said. Al-Hayeh had previously survived two Israeli assassination attempts that killed members of his extended family.

Hamas policemen set up checkpoints on major thoroughfares and roads leading to security compounds, checking suspicious cars and forcing others to slow down.

Dozens of Fatah supporters were rounded up, said Ibrahim Abu Naja, a prominent Fatah leader in Gaza. Abu Naja said Hamas police also raided offices and institutions belonging to Fatah overnight. Abu Naja's own office was raided on Saturday.

The offices of independent lawmaker Ziad Abu Amr and of Zakariya al-Agha, a member of the PLO Executive Committee, were among those targeted. Another senior Fatah leader, Abdel Rahman Hamad, fled his home amid concerns he would be arrested, his family said.

In one attempted arrest, Hamas police fired four rocket propelled grenades at the home of a local Fatah leader and briefly exchanged fire with his guards, witnesses said.

Police then searched the house, but didn't find the wanted man, Mohammed Aweidat.

The Palestinian Center for Human Rights in Gaza reported that some 160 people, Fatah loyalists and members, were rounded up. The Center suggested the number could be higher. Another 40 institutions loyal to Fatah were raided, including a center for disabled, a folkloric center and benevolent charities.

Sawh Abu Seif, a Palestinian cameraman for the German ARD TV network was among those who were rounded up. He was seized from his home by Hamas forces. Abu Seif, 42, is a former Fatah student union member but has been working as a cameraman since the 1990s, once for Reuters and for the past 6 years for ARD.

An unknown offshoot of the Fatah movement, calling itself the Awda Brigades claimed responsibility for the attack in a statement to reporters. But the claim could not be verified independently.

In the West Bank, Abbas aide Ahmed Abdel Rahman condemned the explosion and said the Hamas crackdown was irresponsible.

"These measures empower separation [of Hamas-ruled Gaza and the Fatah-run West Bank] and reduce chances of a national dialogue and of restoring unity of the two parts of the country," he said.

Friday's beachside explosion was the third of the day.

The first went off outside the Al Jazera cafe, killing the perpetrator of the attack and wounding three people. The cafe had been hit twice before this year, presumably by hardline Muslims who target record shops and other businesses seen as symbols of Western influence.

Later, a bomb exploded outside the house of a Hamas lawmaker, Marwan Abu Ras, causing some damage, but no injuries. A Fatah activist was arrested as a suspect.

Gaza has been relatively quiet over the past month because of a cease-fire between Israel and Hamas that went into effect in mid-June.

But the cease-fire has stoked some tensions between Palestinian factions as Hamas has sought to prevent other groups from firing cross-border rockets at Israel.

Gaza also sees internal Palestinian violence, some of it carried out by fundamentalists who oppose what they see as signs of Western cultural encroachment.

In recent years, shadowy groups have firebombed internet cafes, music stores and Christian institutions. The bombings are typically carried out late at night and most have caused no casualties. But in one deadly attack in October 2007, a local Christian activist was murdered.