BEIT LAHIYA, Gaza Strip -- A powerful roadside bomb ripped apart an armored vehicle in a US diplomatic convoy here yesterday, killing three Americans and wounding one in what appeared to be the first fatal attack on American citizens since fighting between Israelis and Palestinians erupted three years ago.
Investigators said they believe a Palestinian militant detonated the explosive by remote control around 10:15 a.m. as the three-vehicle convoy sped south on a main artery in Gaza, escorted by Palestinian security. Israeli officials estimated more than 200 pounds of explosives were used.
The blast flipped the vehicle over and left a large crater in the unpaved road. Witnesses described seeing body parts fly from the vehicle and blood stream from the overturned car onto the street.
US officials said the three men worked for DynCorp, a private security company based in Reston, Va., that provides protection for diplomatic staff. Others in the convoy were described as members of the embassy's cultural section who had traveled to Gaza to interview Palestinian applicants for a Fulbright scholarship.
The US Embassy in Tel Aviv urged the several hundred Americans who work in Gaza to leave immediately, and President Bush strongly condemned the attack.
"Palestinian authorities should have acted long ago to fight terror in all its forms," the president, traveling in California, said in a statement. "The failure to create effective Palestinian security forces dedicated to fighting terror continues to cost lives."
No one claimed responsibility for the bombing. Spokesmen for the two militant Islamic groups in the West Bank and Gaza -- Hamas and Islamic Jihad -- denied involvement. Palestinian leaders condemned the bombing as both immoral and counterproductive.
But youngsters who streamed to the site of the attack from nearby villages picked through the twisted metal with visible delight, grousing about what many Palestinians believe is America's uncritical support for Israel. Dozens of them threw stones at American investigators who arrived at the scene. Although pushed back by Palestinian police, the youths managed to chase away the US investigators.
"People were talking to each other and saying the Americans deserve what has happened to them because they used the veto against the Palestinians," said Muneer al-Dwaik, a Palestinian motorist who came upon the scene, referring to Washington's vote against a UN resolution late Tuesday that would have condemned Israel for building a barrier that cuts into the West Bank.
Dwaik said he saw parts of the car and belongings from inside, including guns, scattered across a large radius. He said the other two American vehicles circled after the explosion and sped back to the Israeli border.
"One of the diplomatic cars was splashed with blood on the right side. There was blood on the ground," said Dwaik, 42. "The smell of petrol burned my eyes."
Fayez Doghmesh, who fixes tires in a shop across the street from the bombing site, said he saw Palestinian police gathering wires from the road after the attack. A reporter for the Associated Press described seeing a gray wire with an on-off switch leading from the scene of the blast to a small concrete room on the side of the road. Doghmesh and other local residents said American vehicles like the ones in yesterday's attack, dark-colored Chevrolet Suburbans with diplomatic license plates, travel in Gaza about the same time every day.
Palestinian militants have used similar bombs against Israeli jeeps and tanks in Gaza, a poor and crowded sliver of land along the Mediterranean. Three Israeli soldiers were lightly wounded in such an incident yesterday.
One US Embassy official said a bomb was set off near an American convoy three months ago, but that incident aside, militant groups have refrained from targeting Americans.
"Hamas's position is not to expand its struggle and Hamas's enemy is only . . . the Israeli occupation," said a spokesman for the group, Adnan Asfour.
Palestinian analysts said a series of recent American decisions and remarks lately had stoked anti-US sentiment in the West Bank and Gaza, including Bush's refusal to criticize Israel's airstrike on Syria this month. But they said most people understood that targeting Americans would only harm Palestinian interests.
"I believe it could have catastrophic results," said Mahmoud Ajrami, a member of the Palestinian National Council. "There's no other power in the world that can impose pressure on Israel to reach a settlement."
The bombing underscored the precarious position of Ahmed Qurei, the recently appointed Palestinian prime minister. Qurei is under pressure from Israel and the United States to dismantle militant groups, but he has been unable to wrest control of the security agencies in the West Bank and Gaza Strip from Yasser Arafat.
Qurei condemned the blast and vowed to "conduct an investigation." Arafat called the bombing "an ugly crime."
The State Department identified the slain Americans as John Branchizio, 36; Mark T. Parson, 31; and John Martin Linde Jr., 30. Their hometowns were not released.
Israel sent tanks into neighboring Beit Hanoun after the blast and kept attack helicopters hovering high over the area for hours as US Embassy officials collected the bodies of the security men and transported them out of Gaza.
Israeli officials said the bombing proves Palestinians should be compelled to disarm militant groups before any progress is made in the international peace plan known as the "road map".
"The Palestinian Authority failed to take any measures whatsoever to dismantle the terrorist infrastructure and to prevent attacks like this one," said Ra'anan Gissin, a spokesman for Prime Minister Ariel Sharon.
Other officials said Palestinians in Gaza had managed to assemble huge bombs from explosives smuggled in underground tunnels running from neighboring Egypt to the southern town of Rafah.
Recent Israeli raids have drawn condemnation from human rights groups, as has Israel's intention to expel 15 Palestinians suspected of militant activities from the West Bank to Gaza. Israel's Supreme Court temporarily blocked the expulsion yesterday until judges can hear their appeals, which are expected within a week.
Sa'id Ghazali and Alon Tuval of the Globe's Jerusalem bureau contributed to this report.