The latest killing was the highest Palestinian daily death toll since the Palestinian intifada began last September.

Calling the killings "a dirty, immoral operation," Palestinian leader Yasser Arafat said Israel would be "harshly judged" for the incident.

There were conflicting reports of the incident, with the Israeli army saying soldiers saw "suspicious figures who were where they were not supposed to be."

But Arafat said four of the five policemen were asleep during the attack. Palestinian witnesses said four policemen were inside a shack while two others were on guard duty outside when Israeli soldiers fired from a building overlooking the checkpoint. The sixth police officer was taken to hospital.

Arafat's comments came on the eve of Nakba or "great catastrophe," an emotionally charged anniversary, when Palestinians lament the May 15, 1948, founding of the Israeli state.

No End in Sight

During a night of intensive violence, thousands of Gaza residents took cover as Israeli helicopters shelled Palestinian police positions and armored vehicles.

Firing was also reported near the disputed Chebaa Farms area near the Israeli border with Lebanon today.

In the West Bank town of Ramallah, tens of thousands of Palestinians marched behind ambulances carrying the bodies of the five policemen chanting, "revenge."

The officers, aged 17 to 29, were killed by shots to the head and chest, Palestinian officials said. They are expected to be buried near their homes in Gaza later this week.

As anger in the streets of the occupied regions mounted, a senior aide to Israeli Prime Minister Ariel Sharon said the attacks were retaliation for Palestinian violence. "Yasser Arafat is trying to impose on Israel negotiations with constant sniping, roadside bombs, and mortar attacks against Israeli civilians," said Dore Gold. "Israel does not accept this formula."

The statement came as the Palestinian Authority today lodged a formal protest with the United Nations Security Council over the killings.

Israel is expected to formulate an official response to a report submitted by an international panel headed by former U.S. Senator George Mitchell. The report calls for a halt to the current round of violence as well as a freeze on the construction of Jewish settlements in the West Bank and Gaza Strip.

But Sharon has already rejected a freeze on the building of settlements.

The current round of violence has killed more than 450 people, mostly Palestinians.