Hundreds of Israeli soldiers searched the border area between the Gaza Strip and Egypt on Thursday for the remains of five soldiers killed in a huge explosion Wednesday. The patrols sparked frequent fighting in which at least 12 Palestinians were killed, Israeli army officials and Palestinian security and hospital officials said.

Seven Palestinian men were killed in a 1 a.m. missile strike by an Israeli AH-64 Apache helicopter and four others died in a second Apache attack at 10:30 a.m., Palestinian security and hospital officials said. In addition, a 19-year-old man was shot to death by an Israeli sniper outside his home, they said.

The deaths on Thursday marked one of the deadliest periods in Gaza since the Palestinians began their uprising in September 2000. Since Tuesday morning, at least 27 Palestinians have been killed and 280 have been injured, while 11 Israeli soldiers have been killed and five wounded in the fighting.

The Israeli losses prompted renewed calls from Israelis for the withdrawal of troops and 7,500 Jewish settlers from Gaza. Prime Minister Ariel Sharon proposed a pullback, but his Likud Party voted the measure down two weeks ago in a nonbinding referendum, even though opinion polls show that as many as 70 percent of Israelis support it. Sharon is trying to revive the plan.

The Maariv newspaper ran a headline on its front page Thursday decrying "The Curse of Gaza." Well-known actor Shlomo Vishinsky, who lost a son in the blast Wednesday, called Sharon a "patsy for the Likud" in Israel's largest daily, Yedioth Ahronoth.

No militant groups claimed to be holding any remains of the soldiers killed in Wednesday's blast -- unlike an incident Tuesday in which militants held soldiers' body parts as bargaining chips. But the process of collecting the bodies was hindered by the large debris area and the hostile, open environment, according to Capt. Jacob Dallal, an army spokesman.

The blast Wednesday occurred in a cleared strip known as the Philadelphi corridor, which separates Egypt and Gaza near the border town of Rafah, an area of sophisticated cross-border smuggling operations.

The explosion occurred about 6 p.m., when a militant from the radical group Islamic Jihad fired a shoulder-launched, rocket-propelled grenade at a convoy of three Israeli armored vehicles that had stopped along the border to blow up the entrance of a smuggling tunnel, according to Israeli army officials and a statement by Islamic Jihad. The rocket hit an armored personnel carrier containing 1,750 of pounds of explosives, causing a tremendous blast that killed five soldiers, injured three others and reportedly sent debris flying a far as half a mile away.

Israeli soldiers fanned out to secure a wide area around the blast site so Palestinian militants would not seize any body parts and hold them for ransom, as happened on Tuesday in a bomb attack in which six soldiers were killed. Jewish tradition considers it imperative to maintain the sanctity of a dead body and collect all of its parts for burial.

Palestinian militants collected body parts in the first attack, including the head of an Israeli soldier, and paraded them through Gaza City, demanding the release of Palestinian prisoners being held by Israel. Images also were shown on Arab satellite television channels. Israeli troops responded with an incursion into the Gaza City neighborhood of Zeitoun in a massive search operation that ended early Thursday when Egyptian intermediaries helped return the body parts from the first blast in exchange for Israel withdrawing its troops.

In the wake of the two explosions, the army has ordered its troops to stop carrying large amounts of explosives in armored personnel carriers pending a review, according to Israeli Army Radio.

At least 15 Palestinians were killed and 245 were injured during the Zeitoun operation. Residents returned Thursday to torn up streets, broken water lines and downed power lines. At least six buildings were demolished during the raid, leaving at least 30 families homeless.

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

Palestinians return to the Zeitoun neighborhood of Gaza City after Israeli forces withdrew from the area. At least six buildings were destroyed during an Israeli operation.Israeli soldiers search for body parts of troops killed in an explosion Wednesday near the Egyptian border.