GAZA CITY, Gaza Strip — Militiamen from the ruling Hamas opened fire on government workers protesting their unpaid salaries yesterday, touching off gunbattles with security forces loyal to the Palestinian president, Mahmoud Abbas. Seven people were killed in the violence.

After the deadly protest in Gaza City, dozens of supporters from Mr. Abbas’s Fatah Party retaliated by ransacking and torching the empty Cabinet building in the West Bank city of Ramallah. The Fatah supporters had earlier marched through the city, the seat of the Palestinian Arab government, burning tires and shouting, “Hamas, out, out.”

Hamas Radio accused Mr. Abbas of stoking the unrest and dividing the Palestinian Arab people. It also attacked his efforts to pressure Hamas to recognize Israel, a move that some say could help to ease crushing international sanctions that have prevented the government from paying salaries.

Mr. Abbas ordered police, most of whom are loyal to Fatah, not to take part in demonstrations. On Saturday, the Hamas-led government deployed all 3,000 Hamas militiamen across the Gaza Strip to stop the widening protests.

Hamas set up its 3,500-member militia in May after losing a power struggle with Mr. Abbas for control of Palestinian Arab security forces. Since then, violence has sporadically broken out between Hamas’s militia — which falls under the control of the Hamas interior minister — and the official police force.

The most serious clash between them yesterday took place near the parliament building in Gaza City.After the crowd of protesters there swelled to include hundreds of police and civilians, Hamas militiamen rushed in, firing guns and anti-tank launchers, and lobbing grenades.

Two people were killed, including a 15-year-old boy, and at least 75 were wounded, hospital officials said.

Militiamen and security personnel — including bodyguards for Mr. Abbas — exchanged fire on two of the main streets of Gaza City near parliament, and gunmen from both sides took positions on nearby rooftops.

Protesters scattered, and schoolchildren sought protection by covering their heads with their schoolbags.

The clashes later spilled over to an area near the president’s residence. Hamas militiamen scrambled up to the rooftop of the nearby Agriculture Ministry and began firing on the presidential guard, killing one.

Hospital officials later reported a three others killed in the violence yesterday, and security officials said an officer whose car came under fire also died.

“We are going to beat with iron fists all those elements who are trying to sabotage the election process of our people, those who are trying to destroy our public properties and close the streets,” a spokesman for the militia, Islam Shahwan, said.

Mr. Shahwan said 25 security personnel were arrested by Hamas militiamen.

“Nothing can justify this violence,” a Fatah spokesman, Tawfik Abu Khoussa, said, blaming the government.

The chief of national security in southern Gaza, Jamal Kayed, said militiamen attacked both his force’s headquarters and its officers.

A government spokesman, Ghazi Hamad, said the violence was “regrettable” but that the Hamas force acted with restraint and was attacked by the demonstrators.

“The protest today was beyond acceptable legal norms and turned truly into lawlessness,” he said.

After the violence in Gaza City, Fatah protesters in Ramallah broke into the Cabinet building there and set fire to a second-floor office.

The militants, forced out by the flames and smoke, then moved to the nearby Education Ministry and torched a car on the way.

Since Hamas ousted Fatah from power earlier this year, Israel and the West have withheld tax payments and foreign aid to try to force Hamas to change its policies.

Protests against the government have grown as the poverty deepened.In an effort to end the economic embargo, Hamas officials have talked of forming a coalition government with Fatah, but the efforts foundered because of Hamas’s refusal to recognize Israel’s right to exist.