Israel has defied a formidable international consensus in favour of a ceasefire in Gaza by opting to continue its unprecedentedly fierce air attacks on Hamas targets and stepping up preparations for a possible ground offensive.

As the security cabinet rejected an EU-backed French proposal for a 48-hour humanitarian halt to the bombing, Prime Minister Ehud Olmert said: “We did not begin the Gaza operation in order to finish it with rocket fire continuing like it did before. Israel has restrained [itself] for years and given plenty of chances for a calm.”

With Palestinian sources putting the total death toll in Gaza at 390, since the bombing beganon Saturday, with 1,600 wounded, Associated Press reported that a long column of tanks and armoured vehicles was visible along an access road to Gaza from Israel, while dozens of other tanks were parked in a field close to the border.

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The Israeli military reported that more than 50 rockets had been fired by Gaza militants yesterday, including further longer-range, reportedly Chinese-made, rockets at the large southern city of Beersheeva which is more than 22 miles from the border. There were no serious casualties as a result by early evening. Four Israelis have been killed since the bombardment began last Saturday.

The Defence Minister, Ehud Barak, had let it be known on Tuesday that he intended to submit the proposal for a halt to the offensive – whose backers include the US – to yesterday’s security cabinet. But, after considerable confusion, he appears to have been persuaded at a meeting which included Mr Olmert and the Foreign Minister, Tzipi Livni, not to do so.

In Gaza City, apartment buildings shook during air strikes on government buildings which the Israeli military said included an office of Ismail Haniyeh, Gaza’s Hamas Prime Minister. The Israeli military said it was not aware of a missile striking an ambulance, which Palestinian sources said had killed two medics. An Egyptian official said Israel has destroyed 120 of between 200 and 400 smuggling tunnels since Saturday.

Mark Regev, Mr Olmert’s spokesman, said Israel would work with international agencies to increase aid to the civilian population. “I don’t detect much criticism from Berlin, Paris and London about hitting Hamas targets. What there is concern about is the humanitarian situation,” he said.

The Israeli human rights organisation B’tselem yesterday reported testimony that a truck destroyed in an air attack on Monday, which the military said was carrying Grad missiles, was in fact carrying oxygen canisters. Eight people were killed in the bombing. Abu Imad Sanur, the owner of the truck, whose son was among the dead, and who denies any connction with militants, told the agency that he and his family had been salvaging the canisters from his metal workshop, which was next to a building that had been bombed. An Israeli official strongly denied the claim and said the military was preparing a full response.

Gordon Brown said: “It is vital that moderation must now prevail – there’s a humanitarian crisis. Of course, the second thing we’ve got to do is secure an immediate and urgent ceasefire.” The Prime Minister said proposals for a ceasefire package being discussed by Arab foreign ministers in Cairo offered “the best way forward”.

The package contains similar elements to those spelled out on Tuesday by EU ministers and the Middle East Quartet. The proposals call for an immediate and sustainable ceasefire, with international monitors guaranteeing the truce and the reopening of border crossings into Gaza. European governments hope that, if the Arab states agree a united position, it would increase the pressure on Hamas to compromise.

But yesterday it was Arab divisions that were on display. The Saudi Foreign Minister, Prince Saud al-Faisal, said: “This terrible massacre would not have happened if the Palestinian people were united behind one leadership speaking in one voice.

“We are telling our Palestinian brothers that your Arab nation cannot extend a real helping hand if you don’t extend your own hands to each other with love.”