This was the first time since the start of the new Intifida that Palestinians used successfully sophisticated explosive for penetrating the Merkava 3. The last time a crewmember was killed in a Merkava was in southern Lebanon about five-and-a-half years ago, when the tank was hit by an anti-tank missile.

Israel Radio reported that in Thursday's attack, the tank's turret was blown off, landing several meters away, and that the blast gouged a 1.5-meter hole in the ground.

The sophistication of the attack was reminiscent of operations conducted by the Iran-backed Hezbollah against Israeli soldiers, forcing Israel to withdrew from Lebanon after 20 years of occupation of a portion of land described as "Security Zone".

"The blow is painful, but I say to you honestly that I am not surprised that it happened" reservist Brigadier General Hanan Bernstein, former head of the IDF's Merkava division and commander of the tank training school, told Israel Radio on Friday.

The main goal of the latest model was to better-protect its four-member crew - driver, gunner, loader-signaler and commander. The tank's protective shell is one of the most closely guarded secrets. In order to increase the tank's chance of survival against bombs or mines that detonate alongside or underneath it, or against hits by anti-tank missiles, an especially thick armor was developed to cover the Merkava. In some parts of the tank, that armor is almost one-meter thick.

Even in roadside bomb attacks in Lebanon over the past decade the armor of Israeli tanks has never been hit hard enough to strike an entire tank crew.

Though it weights about 65 tons, the Merkava 3, equipped with a 1,200 horsepower engine, is considered to be fast, capable of reaching speeds of 65 kilometers per hour. The tank carries 50 shells with a 120-millimeter diameter, mortars, smoke bombs and thousands of rounds of light ammunition.

"The game of cat and mouse, Bernstein said, would continue no matter what changes were made".

Military officials said half an hour before the tank was hit, Palestinians opened fire on a civilian convoy guarded by soldiers and set off a bomb that damaged a bus but caused no injuries. The army sent a tank into the area and a huge bomb exploded under it in what appears to have a planned two-stage gun-and-bomb ambush. Hamas and Fatah claimed responsibility.

The bomb, an unusually large and sophisticated one weighing perhaps scores of kilograms, apparently hit the tank at an unusual angle, experts said. It thus managed to penetrate the armor, according to an initial army investigation of the incident.

The attack will oblige the military to reconsider its regulations on military traffic in the Gaza Strip and is sure to be considered a major victory and morale booster for the Palestinians.

A group including the military wings of Hamas and Palestinian Authority Chairman Yaser Arafat's Fatah faction jointly claimed responsibility for the attack, that analysts said would boos the moral of Palestinians and force Israel to reconsider its occupation policies.

A statement by the Salahedin Brigade, the military wing of the Popular Resistance Committees group, said the attack was in response to Israel's killing on Wednesday of five Palestinian policemen during a raid in the Gaza Strip.

Wednesday's incursion into Palestinian-controlled areas of Gaza, the largest IDF operation in the strip since the intifada erupted more than 16 months ago, was in response to Kassam-2 rockets fired by Hamas militants. Palestinian sources said all Palestinians on Israel's wanted terrorist list had managed to escape the area before the IDF entered.

"The destruction of Mrekava 3 and the killing of three crewmen are a demoralising blow for the Israeli army, already accused by Western and Israeli human rights activists of brutalising Palestinians, and simultaneously criticised at home for doing too little to hald the Palestinian armed uprising", commented an Israel expert.

What concerned more Israel defence experts about the new method used by Palestinians was the killing, on Friday, of Lieutenant-colonel Eyal Weiss, the commander of the elite Duvdevan unit, accused by the Palestinians for the "most dirty works" of the Israeli army in the Palestinian-controlled areas.

In a poll published by Ma’ariv on Friday, 49 per cent of the Israelis said the government had lost control of the security situation, but an equal number expressed satisfaction at Ariel Sharon’s performances.

The destruction of the Merkava 3 came as the Palestinians have also started using "Qasem-I" and "Qasem II" rockets, again adopting Hezbollah’s methods of fighting the Israelis.