RAMALLAH, West Bank (AP) – Hundreds of Palestinian security men loyal to President Mahmoud Abbas went on a rampage against the Hamas-led government Monday, riddling the parliament building and Cabinet offices with bullets before setting them ablaze in retaliation for an attack by Hamas gunmen in the Gaza Strip.

The violence was the most serious in the West Bank since Hamas defeated Abbas’ Fatah movement in legislative elections in January and raised new fears the Palestinians could be headed toward civil war. It also cast doubt on renewed calls for Palestinian unity by the rival factions.

Abbas, a moderate who was elected separately last year, has been locked in a bitter power struggle with Hamas. The dispute has focused largely on control of the powerful security forces.

In Monday’s unrest, hundreds of members of the Preventive Security force shot out the windows of the parliament building before storming the two-building Cabinet complex, where they smashed furniture, destroyed computers and tore up documents. No casualties were reported.

Shooting wildly in the air, the mob then set fire to one of the Cabinet buildings, gutting the fourth floor. When a fire engine approached the scene, one gunman lay on the road, preventing it from reaching the building.

“Every time they touch one of ours in Gaza, we will get 10 of theirs in the West Bank,” said one member of the Preventive Security force. Dozens of gunmen from the Al Aqsa Martyrs’ Brigades, a pro-Fatah militia, joined the mob.

The crowd also set fire to the parliament building and a Hamas office. Both blazes were quickly contained. Abbas’ presidential guard later arrived to guard the burnt-out parliament and Cabinet buildings.

Late Monday, Fatah gunmen briefly abducted a Hamas lawmaker, Khalil Rabei, after attacking his office and setting it on fire. Rabei said he was kicked and threatened before he was released.

Abbas’ personal guard granted refuge to Rabei and nine other Hamas lawmakers, and was ordered to escort the men home safely.

The rampage in Ramallah followed an earlier attack by Hamas gunmen on a Preventive Security installation in Gaza. The attack set off daylong clashes that left two people dead and 14 wounded.

Most of the Palestinian infighting in recent weeks has occurred in Gaza, Hamas’ stronghold. Monday’s incident signaled that Fatah is now ready to move the conflict to its West Bank power center.

Abbas was in Gaza at the time of the rampage, where he has been holding negotiations with Hamas in hopes of ending the political deadlock.

“The president strongly condemns the attacks and the assault against the public institutions and the building that took place in the West Bank tonight,” said a statement issued by Abbas’ office.

“Whatever is going on must be stopped,” said Nabil Abu Rdeneh, a close aide to Abbas. “Everybody must obey the law.”

Officials said Abbas had appointed a retired commander to serve as a military adviser and liaison to the Hamas-run Interior Ministry. The appointment of Lt. Gen. Abdel Razek Majaide could help ease tensions. Majaide is respected by Fatah and Hamas alike.

Internal tensions have heightened since Abbas scheduled a July 26 referendum on a plan that calls for recognition of Israel. Abbas has endorsed the plan as a way out of the stalemate. But Hamas objects to the vote.

In a conciliatory gesture, the Hamas-dominated Palestinian parliament pulled back from a plan to block the referendum, delaying a vote on the issue until June 20 to allow negotiations to continue. But the violence cast serious doubts on the efforts to bridge the gaps.

Early Tuesday, several thousand Hamas supporters demonstrated outside the Palestinian parliament building in Gaza. They condemned the violence in Ramallah, rejected the referendum and threatened retaliation against the Preventive Security forces.

“What happened today in Ramallah is very shameful and I think the president did not use all his efforts to prevent it,” said Hamas spokesman Sami Abu Zuhri.

Seeking a way out of the infighting, Abbas last weekend scheduled the referendum on a plan calling for a Palestinian state alongside Israel, implicitly recognizing the Jewish state.

Abbas believes a unified political platform by Palestinian factions would help end crushing international sanctions against the Hamas-led government and allow him to restart peace talks with Israel.

Hamas, which is sworn to Israel’s destruction, opposes the referendum vote. But it has entered a “dialogue” with Abbas over the plan. The sides were meeting late Monday when violence erupted in the West Bank.

“We want to get to a situation of calm and prevent the shedding of Palestinian blood,” said Hamas lawmaker Khalil al-Haye.

Abbas is pushing forward with the referendum despite calls for a delay following an explosion on a Gaza beach Friday that killed eight civilians.

Palestinians said an Israeli artillery shell caused the explosion, which has inflamed passions against Israel. Israel is conducting an investigation and has suggested its army wasn’t responsible.

Israel-Palestinian violence has escalated since the beach explosion, with Hamas officially calling off a 16-month truce.

Hamas militants have fired several dozen rockets at southern Israel, including one that landed in the southern town of Sderot on Monday, slightly wounding a woman in the shoulder. A total of three people have been wounded in the recent rocket attacks, including one man in serious condition.

The end of the truce has raised concerns that Hamas could resume the suicide attacks. But with Hamas now the governing power, it might pressure its military wing to avoid deadly confrontation with Israel for fear of deepening its international isolation.