Ramallah, West Bank ? A landslide victory by the Islamic militant group Hamas in Palestinian elections unnerved the world Thursday, darkening prospects for Mideast peace and ending four decades of rule by the corruption-riddled Fatah Party.

The parliamentary victory stunned even Hamas leaders, who mounted a well-organized campaign but have no experience in government. They offered to share power with President Mahmoud Abbas, the Fatah chief, who said he may go around the new government to talk peace with Israel.

Underscoring the tensions between the secular Fatah and fundamentalist Hamas, some 3,000 supporters of the militant group marched through Ramallah and raised their party’s green flag over the Palestinian parliament. Fatah supporters tried to lower the banner. The two sides fought for about 30 minutes, throwing stones and breaking windows in the building.

Abbas, who was elected last year to a four-year term as president of the Palestinian Authority, has yet to decide how closely to work with a group that built its clout through suicide bombings. But his Fatah Party decided not to join a Hamas government, Fatah legislator Saab Erekat said.

“We will be a loyal opposition and rebuild the party,” Erekat said after meeting with Abbas.

Palestinian supporters of Hamas celebrate their victory Thursday in parliamentary elections in the West Bank town of Ramallah. The Islamic militant group won a majority in parliamentary elections as Palestinian voters rejected the longtime rule of the Fatah Party, throwing the future of Mideast peacemaking into question, officials from both major parties said.

Hamas won a clear majority in Wednesday’s vote, capturing 76 of the 132 seats in parliament, according to official, near-complete results released Thursday. The results of the popular vote were not announced.

Four independent candidates backed by Hamas also won seats. Fatah, which has dominated Palestinian political life since the 1960s but alienated voters because of rampant corruption, won 43 seats. The remaining went to smaller parties.

Palestinians across the Gaza Strip and West Bank greeted the election results with joy, setting off fireworks and firing rifles in the air.

But leaders across the world demanded that Hamas, which is branded a terror group by the United States and European Union, renounce violence and recognize Israel.

“If your platform is the destruction of Israel, it means you’re not a partner in peace, and we’re interested in peace,” President Bush said in Washington.

Acting Israeli Prime Minister Ehud Olmert said Israel would not negotiate with a Palestinian government that includes Hamas members, and senior Cabinet officials had an emergency meeting to discuss the repercussions of the vote. Acting Foreign Minister Tzipi Livni asked the EU not to deal with a “terror government.”

Palestinian supporters of Hamas celebrate their victory in parliamentary elections in the West Bank town of Ramallah, Thursday, Jan. 26, 2006. Hamas supporters briefly raised their flag over the Palestinian parliament and rushed into the building, amid clashes with Fatah loyalists. The two camps threw stones at each other, breaking windows in the building, as Fatah supporters briefly tried to lower the green Hamas banners. It was the first confrontation between Hamas and Fatah since the Islamic militant group won parliament elections on Wednesday.

Hamas leaders immediately took to the international – and even Israeli – airwaves to send out a moderate message.

“Don’t be afraid,” Ismail Haniyeh, a Hamas leader, told the BBC.

Mahmoud Zahar, another Hamas leader, said the group would extend its year-old truce if Israel reciprocates.

“If not, then I think we will have no option but to protect our people and our land,” he said.

At a victory news conference late Thursday, however, Haniyeh said Hamas will “complete the liberation of other parts of Palestine.” He did not say which territories he was referring to or how he would go about it.

Hamas has largely adhered to the cease-fire declared last February, while a smaller militant group, Islamic Jihad, carried out six suicide bombings against Israelis during that period.

Abbas said he remained committed to peace talks and suggested they be conducted through the Palestine Liberation Organization rather than the Palestinian Authority. That could help him sidestep a Hamas-run government in peace talks.

Hamas’ victory was cheered in the Arab world, though many said they feared the group would become even more radical under pressure from its hard-line backers, Syria and Iran.