An Israeli air strike on a northern Gaza refugee camp killed at least four Palestinian militants yesterday, the fifth day of one of Israel's bloodiest offensives in Gaza in four years of conflict. Witnesses and medics said the dead included a senior Hamas field commander.

The early morning raid was launched shortly after Israel's army chief warned that the incursion into Gaza would last “as long as necessary” to halt rocket attacks against Israel. Fifty-nine Palestinians, at least 38 of them militants, have been killed in fighting since Israel launched the offensive five days ago after two Israeli toddlers were killed in a rocket strike on the Israeli border town of Sderot.

“Our mission is to remove Sderot from rocket fire range,” Israeli commander Colonel Eyal Izenburg told Israel Radio. At the United Nations, UN Secretary-General Kofi Annan urged Israel to halt its raids in Gaza, “which have led to the deaths of scores of Palestinians, among them many civilians”. He also called on Palestinian leaders to help curtail rocket fire.

Israeli Prime Minister Ariel Sharon said the army would expand a “buffer zone” in northern Gaza to spare Israeli towns rocket fire and ensure that militant groups were crushed ahead of his planned withdrawal from the Gaza Strip next year. “Evacuating the Gaza Strip is a plan that will be carried out and all orders have been given to ensure that there will be no fire at the time of the evacuation and I believe not after that either,” Sharon said.

Sharon needs to halt the rocket strikes to counter rightists who say that evacuating troops and Jewish settlers from Gaza will encourage more attacks. Nearly 200 tanks and armoured vehicles have seized 9 square km (3 square miles) of the northern strip and carried out raids deep into teeming Jabalya refugee camp, a militant hotbed. Other armour has encircled the town Beit Hanoun.

In the strike before dawn yesterday, an Israeli missile killed four Palestinian militants, including a Hamas field commander, in a strike in Jabalya refugee camp where they were planting bombs. The bodies were blown to pieces.

<B>“Not days, but weeks” </B>

Israel's military chief Moshe Yaalon told reporters on Sunday while visiting troops in Gaza on Sunday the raid had been “successful”, and Israel had hit seven gangs of militants involved in firing rockets, including one on a donkey cart. “We will continue this operation for as long as necessary,” to prevent rocket attacks, he said. “The forces are prepared to carry out this operation not in terms of days, but weeks.”

Ismail Haniyeh, a Hamas leader, suggested the militants might be ready to reconsider firing rockets at Israel, telling reporters they “would seriously study their methods” if Israel halted all military action in Gaza.

But other militants were determined to appear to be driving Israel out of Gaza, given Sharon's plan to pull soldiers and settlers out of the land Israel occupied in the 1967 Middle East War. “The Qassam rockets will not stop as long as the occupation exists,” Mushir al-Masri, a spokesman for Hamas, told a rally of 4,000 in Gaza City late on Sunday.