Palestinian militants killed 13 Israeli reserve soldiers in an ambush in the Jenin refugee camp in the West Bank yesterday, the heaviest single blow to the Israeli army in 18 months of bloodshed.

Israeli military commentators said the Palestinian fighters blew up a booby-trapped building which collapsed on one group of soldiers, after which gunmen opened fire on a second army unit that came to their rescue.

The army said it believed a Palestinian suicide bomber was involved in the operation as well as nearly 20 other militants.

"An army patrol by reserve soldiers was ambushed during operations in the Jenin refugee camp. The ambush included the use of explosive devices detonated against them and gunfire from nearby rooftops," the army said in a statement.

"Thirteen soldiers were killed," it said, adding that seven other soldiers were wounded, one of them critically.

The toll was the highest in a single attack against the Middle East`s strongest army since a Palestinian uprising against Israeli occupation started in September 2000.

The deaths occurred yesterday morning but were not disclosed until the families of the soldiers were notified.

Palestinian Information Minister Yasser Abed Rabbo said the army was attacking the camp with helicopters and razing buildings with bulldozers "to finish this camp by tonight".

"They are short of time and they want to gain time tonight in order to achieve what they believe is a total victory over the Old City (of Nablus) and Jenin camp," he told Reuters.

Palestinian officials estimate more than 100 Palestinians have been killed in battles inside the camp of 13,000 people over the last week.

They have accused Israel`s army of carrying out a massacre in the camp. Israeli officials say they are engaged in heavy fighting against what they estimate are hundreds of militants holed up amid a civilian population.

Before the latest ambush, nine Israeli soldiers had been killed inside the camp and neighbouring town.

"There was no massacre. There was a very tough war there and I can tell you there were many people (Palestinians) who wore explosives belts to kill our soldiers," Israeli Foreign Minister Shimon Peres said.

Ron Ben-Yishai, military affairs correspondent for Israeli Channel One television who is regularly briefed by the army, said the ambush took place after soldiers entered one of the houses in the refugee camp "and a ring of several explosives were detonated all at once, which killed several soldiers.

"The building collapsed on them - the terrorists had no problem with collapsing a building on top of our soldiers - and then when the rescue force came... they opened fire on them from all of the surrounding rooftops," he said.

In the course of a week of battles, Israeli infantry soldiers had advanced through the crowded camp house by house, backed up by frequent helicopter strikes, residents said.

They said Israeli bulldozers had smashed their way through buildings to clear a path for tanks to pass through the camp`s narrow alleys where fighting has raged.

Witnesses said dozens of corpses of Palestinians killed in the fighting remained in the streets and only a few ambulances had managed to enter the camp to evacuate the wounded.

Some of the camp`s residents managed to flee during the fighting, while those who remained struggled to find food and water during the siege.

Israeli military commentators have referred to the Jenin camp as the "cradle of the Intifada", or uprising, a stronghold for Palestinian militants behind a series of suicide bombings against civilians in Israel.

The army said many of the houses had been booby-trapped and that the camp contained many facilities for producing bombs.