Sunday's deafening explosion sent shock waves kilometres away. It was the largest such demolition since the start of the Intifada three years ago.

The 13-storey partly constructed buildings were dynamited after troops at night evacuated an estimated 2000 Palestinian residents from the Gaza Strip town of al-Zahra.

A flash of light was seen against the night sky as the simultaneous blasts sent all three buildings tumbling down and a cloud of grey smoke from the rubble rose into the air.

Apartments in Gaza City shook from the force of the blast which took place at about 02:30 (0030 GMT) and could be felt across the border in Israel.

Message

"It was very accurate, very well done. I hope there is no collateral damage. I hope it will be a good message to the Palestinian Authority not to let their infrastructure be used for terror," said Brigadier-General Gadi Shammi, commander of Israeli forces in the Gaza Strip.

Security sources said the buildings were used by Palestinian groups to observe troop movements before launching a resistance attack on the nearby Jewish settlement of Netzarim on Friday in which three soldiers were killed.

"It was very accurate, very well done. I hope there is no collateral damage."

Brigadier-General Gadi Shammi,
Israeli army

Leaflets in Arabic were distributed to residents in the hours before the explosion saying: "You must leave your homes immediately until the end of this operation.

"The army is going to blow up some sites. Please leave your windows open, turn off electrical devices and go to the southern part of your neighbourhood. Anyone who stays is risking his life. Anyone seen with a weapon will risk his life." 

Friday attack

One security official said plans to demolish the buildings were drawn up about a year ago, but the decision to implement them was taken only after Friday's attack, which was claimed by the Hamas and Islamic Jihad.

"We gave them a chance," the source said. "We expect buildings owned by the Palestinian Authority will not be used for terrorist activities, but after the raid on Friday we saw that we could not let this go on."

Senior security sources said all the several hundred settlers living at Netzarim had taken refuge in bomb shelters while the Gaza buildings were being blown up.

Hundreds of Israeli troops, including demolition experts and humanitarian liaison officers, were deployed in the operation to evacuate residents living in a 400m radius of the three buildings earmarked for destruction.

Commanders monitored the situation on live video from a truck, several kilometres from the scene.