Israeli troops also killed an 8-year-old girl and wounded seven other Palestinians with submachine gun fire in the Gaza Strip's Khan Younis refugee camp, witnesses and hospital officials said. The girl, Aya Fayad, was shot in the chest by soldiers firing at the camp from a nearby military base.
Soldiers fired at an area where Palestinian militants were detonating roadside bombs on a patrol route, the army said. Militants in the same area later fired three mortar shells at a Jewish settlement, damaging a house but injuring no one, the army said.
The Palestinians asked for the United States to intervene. The strikes, coupled with a Jerusalem suicide bus bombing on Aug. 19 that killed 21, destroyed a cease-fire declared by militant group on June 29 and have seriously jeopardized the peace plan toward Palestinian statehood.
In Saturday's attack, the Israeli helicopters fired four missiles at a pickup truck carrying the two Palestinian men, witnesses said. It was the fifth Israeli missile strike aimed at Hamas militants in 10 days.
The vehicle had been moving slowly in traffic when it was hit and burst into flames, witnesses said. Rescue workers rushed to remove the bodies, including one that was badly burned and missing a leg. Two bystanders also were wounded.
"A missile came and hit the car from the front, followed by another two. I saw one of the men inside the car jump out the window, but another missile hit him," said Balal, 35, a witness who gave only his first name.
The two were identified as Abdullah Akel, 37, and his assistant Farid Mayet, 40, both members of the Hamas military wing, Izzedine al-Qassam.
Akel, a leading field commander in central Gaza, had fired mortar shells and homemade Qassam rockets at Israeli towns and Jewish settlements, and was preparing to fire more rockets when he was killed, the army said. Israel had jailed him for his membership in Hamas during the first Palestinian uprising, between 1987 and 1993.
Waving green Hamas banners and calling for revenge, some 5,000 Palestinians marched through the Nusseirat and Bureij refugee camps in a funeral procession for the two men.
An armed Hamas member told mourners that Israeli Prime Minister Ariel Sharon "will soon receive a very painful message from the Hamas military wing in retaliation for his crimes against the Palestinian people."
Israel stepped up its campaign against militants following the Jerusalem bus bombing, for which Hamas claimed responsibility. Since then, Israel has killed 10 Hamas militants including the two on Saturday.
Palestinian Information Minister Nabil Amr said the missile strike was "part of the comprehensive war against the Palestinians" and blocked the resumption of peace negotiations.
"We hope that our friends, the Americans, will intervene in order to contain this deterioration of the situation," Amr said.
Israel will continue to strike down Palestinian militants so long as the Palestinian Authority does nothing to rein them in, Foreign Ministry official Gideon Meir said.
"We cannot expose our children to the continuous massacre which we witnessed in Jerusalem," Meir said. He accused Palestinian Prime Minister Mahmoud Abbas of failing to fulfill commitments under the road map.
Hamas members fired a Qassam rocket at the Israeli town of Ashkelon last week, prompting Sharon to order the military to take all steps to stop the attacks.
Dozens of Hamas activists vowed revenge on Saturday as they gathered around a hospital where the victims were taken, while Palestinian boys stood on the wrecked pickup's roof, chanting "Hamas."
Hamas issued leaflets after Israel's initial missile strikes this month urging members to wear disguises and move about less frequently to avoid becoming targets. Hamas leaders have turned off their cell phones and have largely stopped appearing at public events.
Abbas has said Israel's missile strikes make it virtually impossible for him to crack down on militant groups, a requirement under the peace plan.
Abbas' power is rapidly dissipating amid the escalating violence and stalled talks. On Saturday, dozens of armed men loyal to Arafat turned out in the Gaza Strip to block the appointment of an official to replace one of Arafat's staunch supporters.
Sakher Basseso, governor of the northern Gaza Strip, had been chosen to take over as chairman of the body in charge of 70,000 civil servants but didn't show up. And the current head of the General Personnel Council, Arafat backer Mohammed Abu Sharia, refused to go.
Basseso was picked by the Cabinet on Wednesday to take over the job.
Basseso, who has tried to mediate in the dispute between Abbas and Arafat, declined to comment about why he didn't show up Saturday, calling it an internal matter.
Arafat reluctantly appointed Abbas, his deputy in the PLO, to be the Palestinians' first prime minister in April under heavy pressure from Israel and the United States, which have refused to deal with Arafat and want an alternative leader.
Arafat has refused to give Abbas full control of security forces, undermining efforts to crack down on Palestinian militant groups.