COLUMNS of Israeli tanks and ground forces roared across the border into northern Gaza under cover of darkness in the first step of a full-scale land invasion last night.

Their mission was to destroy rocket launch facilities and capture or kill the Hamas leadership, the militant Islamists who gained control of the territory 18 months ago.

The incursion, on day eight of the war in Gaza, followed hours of artillery barrages aimed at clearing the way for the 10,000 Israeli troops who had massed on the border.

In a three-pronged attack three brigades entered Gaza. Tracer fire could be seen and Israeli television reported fierce clashes. Residents in Gaza City reported heavy bombing.

The troops, supported by helicopter gunships, advanced on the heavily armed refugee camp at Jabaliya, a Hamas stronghold.

In early clashes Palestinian sources claimed that several Israelis had been killed along with a Palestinian child. The Israelis claimed “dozens” of Hamas fighters had died.

Israel announced a call-up of tens of thousands more reservists. Tzipi Livni, foreign minister and candidate for prime minister, threatened further escalation if Hamas hit back.

“The moment they fire we will respond with great force,” she said. “It could be that several operations will be needed.”

Ehud Barak, the defence minister, said: “We are not war hungry but we shall not allow a situation in which our villages, towns and civilians are constantly targeted by Hamas.

“We restrained ourselves for a long time but now is the time to do what needs to be done.” The operation, he said, “won’t be easy and it won’t be short”. In a veiled warning to Hezbollah, the Islamist militia in Lebanon, he said: “We hope the northern front will remain calm, but we are prepared for any possibility.”

Israeli military officials said their mission was to eliminate the Hamas rocket launch units.

“The objective at this stage is to destroy the terrorist infrastructure of Hamas in . . . order to greatly reduce the quantity of rockets fired at Israel,” said Major Avital Leibovich.

Inside Gaza, Israeli special forces of the Shaldag (kingfisher) and Duvdevan (cherry) units were tracking down leading figures in the military leadership of Hamas. Israeli military planners would like to “behead” the organisation without becoming entangled in a prolonged occupation.

Leaflets dropped earlier in the day over Gaza City and the border areas urged Palestinians to flee their homes. “For your own safety, you are required to leave the area immediately,” stated the warning from the Israel Defence Forces.

An Israeli airstrike yesterday killed Abu Zakaria al-Jamal, a senior Hamas military commander.

Later, in one of at least 30 airstrikes on Gaza, 13 Palestinians, including children, died when an Israeli jet bombed a mosque in Beit Lahiya. Hamas yesterday launched more than two dozen rockets.

Israel launched its ground offensive because despite more than 750 air attacks last week, it had failed to stop the rockets. Inside Gaza there were desperate scenes with no bomb shelters and few places to flee. Food, water and medical supplies were all running short for the strip’s 1.5m residents.

David Miliband, the foreign secretary, issued a statement saying: “Unfolding events show the urgent need for the immediate ceasefire that we have called for . . . We are determined to work as quickly as possible for a durable ceasefire which must include an end to the smuggling of arms into Gaza and the opening of the Gaza crossings.”

Thousands of protesters converged on Whitehall yesterday and other protests were held throughout the Middle East, Asia and Europe.

The United Nations secretary-general, Ban Ki-moon, called for an immediate end to Israel’s ground operations. The UN security council was due to meet early today to consider the situation while Nicolas Sarkozy, the French president, is due to visit Tel Aviv early this week with a ceasefire proposal.

During the Israeli army’s Operation Cast Lead, over 460 Palestinians have been killed. More than 2,100 have also been wounded. Hamas has launched more than 400 rockets, killing four Israelis.

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