Palestinian guerrillas detonated a bomb under an Israeli armored personnel carrier in the Gaza Strip early Tuesday, killing six soldiers in one of the deadliest attacks on Israeli troops in 18 months, Israeli army officials and Palestinian witnesses said.

The bombing, which occurred at 6:30 a.m., followed a night of running gun battles between dozens of Palestinian militants and Israeli troops, tanks and helicopters. Fighting continued throughout the day, and at least seven Palestinians were killed and 120 injured, according to Jumaa Saqqa, a spokesman for Shifa Hospital in Gaza City.

The killing of the six soldiers marked the highest one-day death toll for the Israeli army since November 2002, when nine soldiers and three settlement security officers were killed in an ambush by Palestinians in the West Bank city of Hebron.

The radical groups Hamas and Islamic Jihad each asserted responsibility for the bombing. Islamic Jihad's statement said the device contained 110 pounds of explosives; an Israeli government official said the military estimated it to have been about 220 pounds.

An Israeli army spokesman said the personnel carrier was carrying explosives, which apparently magnified the intensity of a blast that tore the vehicle into small pieces of scrap metal. For several hours, fighting prevented Israeli soldiers from retrieving the remains of the vehicle's crew, witnesses said.

Palestinians paraded through several Gaza neighborhoods displaying body parts, and Palestinian television crews filmed men identified as members of Islamic Jihad holding aloft the head of an Israeli soldier in an empty rice bag. News services later quoted a militant leader as saying the remains would not be turned over until Israel halted raids into Gaza and opened talks on releasing Palestinian prisoners.

"The way they behaved with the bodies of our soldiers -- and they did it in front of the cameras -- proved to the world what we are saying: that we are dealing with barbarians," Justice Minister Yosef Lapid said in an interview.

Secretary of State Colin L. Powell called Foreign Minister Silvan Shalom to express condolences "for the very difficult situation faced by Israeli forces there today," according to Richard Boucher, a State Department spokesman.

"I think we're all very concerned, shocked by the reports we've seen out of Gaza," Boucher said.

Prime Minister Ariel Sharon of Israel scheduled a meeting of his security cabinet Tuesday night to discuss how to respond, his office said in a statement.

The killings appeared likely to intensify debate about Sharon's proposal to remove 7,500 Jewish settlers and thousands of troops from the Gaza Strip, which is populated by about 1.2 million Palestinians. Members of Sharon's Likud Party rejected the plan in a non-binding referendum nine days ago, but Sharon has vowed to pursue it.

Much of the Israeli opposition to Sharon's proposal comes from occupants of Jewish settlements in Gaza and the West Bank and their supporters. Others say that because the plan is not part of a negotiated peace agreement, it would be seen as rewarding Palestinian terrorism and encourage more fighting.

Ephraim Yaar, a pollster and political scientist at Tel Aviv University, said Tuesday's killings "may convince the government, particularly Sharon, to be more decisive about his plan and say that they are going to implement it" by ignoring the referendum and taking the plan directly to Sharon's cabinet or to Israel's parliament. "The effect may be to speed the plan up or make the Israeli government more resolved," Yaar said.

Saeb Erekat, the chief Palestinian negotiator with Israel, said Sharon's disengagement plan was partly to blame for Tuesday's bloodshed.

"If you don't have a negotiating process, you have a conflict process and a military escalation process," he said, "and what we are seeing today in Gaza is very dangerous, because it's a major escalation that's going to lead to more of the same."

Erekat said the Palestinian prime minister, Ahmed Qureia, received a letter Tuesday from President Bush urging him to back Sharon's Gaza withdrawal plan and reiterating that the United States favored a two-state solution to the Israeli-Palestinian conflict and implementation of the peace plan known as the "road map."

The letter also said that "the objective of the peace process was to end the occupation that began in 1967," Erekat said, adding that it stated that the United States would not prejudice final status issues. Bush also asked Qureia to strengthen the Palestinian Authority's security agencies. "It was a good letter," Erekat said.

The fighting in Gaza began shortly after midnight when undercover Israeli soldiers in unmarked cars entered the southern Gaza City neighborhood of Zeitoun, according to an Israeli army spokesman and Palestinian witnesses. The army spokesman said the move preceded an operation to locate and destroy weapons workshops.

Palestinian residents and security sources said that Palestinian soldiers and militants identified the occupants of the cars as Israelis, at which point the Israeli soldiers called in helicopters and tanks.

The Israeli military said an attack helicopter fired a missile at a group of men who were spotted trying to bury a bomb along the side of a road. Palestinian witnesses said that five missiles were fired at several groups, killing four people and wounding dozens.

Sources in the Palestinian security services and militant groups said the bombing of the armored personnel carrier reflected a new tactic being employed by the guerrillas: attacking Israeli forces and planting bombs while a firefight is underway, then trying to lure the Israelis to the area where the bombs are buried.

Special correspondent Islam Abdulkarim in Gaza City contributed to this report.

Israeli soldiers rest following an incursion in the Gaza Strip, during which a bomb exploded under an Israeli armored vehicle and killed six soldiers, the highest one-day death toll for the army since November 2002.