Top Hamas fugitives lobbed grenades and fired automatic weapons today to push back Palestinian security forces storming their hideout, leaving six dead in the bloodiest clash since the Palestinian president launched a crackdown on Hamas in the West Bank two years ago.

Two top Hamas militants - on the run from Israel for years - were among those killed, along with an unarmed Hamas supporter and three Palestinian policemen.

After the hours-long battle, hundreds of spent bullet casings, puddles of blood and tear gas canisters were visible at the hideout, a two-story building in the northern West Bank town of Qalqiliya. Parts of the walls were burned down.

The Islamic militant Hamas immediately hurled angry accusations at the Western-backed president, Mahmoud Abbas, accusing him of betraying Palestinians resisting Israeli occupation and threatening revenge. Relations have been sour since Hamas seized Gaza by force two years ago, leaving Abbas only in control of the West Bank.

The arrest raid underscored Abbas' determination to rein in militants as part of his obligations under the U.S.-backed "road map" peace plan.

The shootout came just three days after Abbas met at the White House with President Barack Obama and renewed a pledge to honor these commitments. The U.S. has been training Abbas' elite forces to help him affirm his control of the West Bank and prepare for eventual statehood.

Despite Hamas' threats of reprisals, it was not immediately clear whether it would change its tactic of lying low in the West Bank while it weathers Abbas' crackdown. Since Hamas' Gaza takeover, Abbas' security forces have detained hundreds of Hamas supporters in the West Bank and closed the group's institutions and charities.

The Qalqiliya clash began late Saturday when Palestinian troops surrounded a hideout of Mohammed Samman, a leader of Hamas' military wing, Izzedine al-Qassam, and his assistant, Mohammed Yassin. Both had been on Israel's wanted list for six years, Palestinian security officials said.

Initially, about two dozen officers stormed the house, breaking down the door, said a policeman who had participated in the raid, but spoke on condition of anonymity because he was not authorized to speak to reporters. The Hamas men lobbed a grenade and opened automatic fire, killing three officers and wounding two critically, he said. Other officers fled, then brought in reinforcements.

The ensuing battle lasted until midmorning Sunday. Police say they found bombs, suicide belts and bullets in their search of the house.

Qalqiliya, which elected a Hamas mayor several years ago, was tense Monday. Women gathered near the scene heaped insults on policemen. Sporadic gunfire erupted in other areas of town, and police said the shots came from Hamas loyalists targeting officers, though there were no reports of injuries.

Security officials seized the bodies of the Hamas militants, fearing a public burial would turn into angry protests against the Palestinian Authority. Muslim tradition demands the dead should be buried quickly.

Hamas officials in the West Bank said that some 40 loyalists of the group had been arrested in Qalqiliya in the past week as part of the search for the top two fugitives.

In Gaza, Abu Obeida, a spokesman for the Hamas military wing, threatened "tough and harsh reprisal."

Ehab Ghussein, a spokesman for the Interior Ministry in Gaza, said Abbas' security forces have betrayed those fighting Israeli occupation.

But Abbas aide Nabil Abu Rdeneh said going after militants is key to one day setting up a Palestinian state. "To build our country and our state, we need to have one authority, one gun, one law," he said.

Hamas opposes Abbas' policy of trying to negotiate a peace deal with Israel. In recent months, Abbas and Hamas have tried to reach a unity deal, but talks have run aground over Hamas' refusal to recognize Israel and renounce violence, a precondition for joining a coalition with Abbas supporters.

Last year, 26 Palestinians were killed during Fatah and Hamas attempts to crack down on their rivals, said the Gaza-based Palestinian Center for Human Rights.