Israel cautioned over raid

Dozens of Palestinians were rushed to hospital

The United States and the United Nations have urged Israel to exercise restraint as troops continue a major offensive against two Palestinian refugee camps in the West Bank.

At least 12 Palestinians and one Israeli soldier died in the Israeli attacks on the Jenin and Balata camps on Thursday, which involved tanks and helicopter gunships.

We've been in touch with the Israeli Government to urge that the utmost restraint be exercised to avoid harm to the civilian population

US State Department

Palestinian officials said they were the fiercest assaults on refugee camps since the start of the Palestinian uprising 17 months ago.

Fierce clashes continued into Friday, with Israeli troops launching a fresh attack on the Jenin camp. At least three Palestinian fighters were wounded, witnesses said.

The Israelis say their aim is to arrest militants and destroy facilities where missiles and explosives are made.

US State Department spokesman Richard Boucher said it was "extremely important that every possible effort be made to avoid harm to civilians".

"We've been in touch with the Israeli Government to urge that the utmost restraint be exercised to avoid harm to the civilian population."

But he also voiced satisfaction that an Israeli-Palestinian security meeting took place on Thursday.

UN Secretary General Kofi Annan said Israeli troops should leave the camps immediately.

"I implore both sides to refrain from further actions which may endanger yet more civilian lives," he said.

Hunt for militants

Israel says it is determined to show that Palestinian militants cannot take refuge in the narrow alleyways and breeze-block buildings of the camps.

Clashes raged all day

The assault began before dawn and clashes with armed Palestinians raged all day.

Israeli soldiers conducted house-to-house searches, reportedly breaking through walls of adjoining properties to avoid exposure to Palestinian militants.

Palestinian gunmen in Beit Jala near Bethlehem opened fire at the nearby Jewish settlement of Gilo in retaliation for the raid.

The new offensive - after a suicide bombing on Wednesday night at an Israeli army checkpoint in the West Bank - overshadowed a Saudi peace initiative aimed at ending the violence.

More than 80 Palestinians were wounded in the Israeli assault, according to Palestinian medical sources.

Palestinian warning

Israeli troops also occupied a United Nations-run school on the edge of Balata - but the army firmly denied reports that its soldiers were trapped there, surrounded by militants.

Marwan Barghouti, the head of the Fatah movement aligned to Palestinian leader Yasser Arafat, described the Israeli offensive as a "massacre".

"We warn Israel that if it does not withdraw its forces in the next few hours, the Palestinian side will retaliate against Israelis everywhere in the occupied territories," Mr Barghouti said.

"I call on all national forces to unite against this Israeli escalation and come forward to defend their brothers in Balata and Jenin," he said.

A similar warning was issued by the al-Aqsa Martyrs' Brigade - the militant group linked to Fatah which on Wednesday said it was behind a female suicide attack that wounded two Palestinians accompanying the bomber and at least three Israeli policemen.