Graphic: in the firing line | Cockpit Video: Israel's aerial onslaught

Israel warned today that the aerial attack on Gaza, which has now entered its fourth brutal day, is only “the first of several” military stages intended to wipe out Hamas.

As the army said it was ready to launch a ground incursion and tanks and infantry forces massed on the border, Israeli officials claimed the military “has made preparations for long weeks of action”.

Ehud Olmert, the Israeli Prime Minister, upped the stakes further today when he said he had informed Shimon Peres, the country's ceremonial president, that the current aerial phase of the operation was the “the first of several stages approved by the security cabinet”.

Hamas continued to fire rockets back at the Jewish state as Israeli forces carried out a fourth day of attacks on the Gaza Strip, broadening the offensive to include naval as well as aerial bombardments. But as Britain and other nations called for an end to the violence, there were signs that Hamas was feeling the strain with claims that its leader-in-exile was ready to renew a ceasefire that expired ten days ago.

Rhetoric from Jerusalem has hardened, however, with Meir Sheetrit, the Interior Minister, claiming “there is no room for a ceasefire” with Hamas until the threat of rocket fire had been removed.

Fires burned across Gaza City today where five government buildings were badly damaged in air attacks after Israel pledged to destroy any building with links to Hamas. The Islamists took lone control of Gaza after launching military action to force out the group's rival Fatah, with which it had formed a unity government, in a military coup in summer 2007. Hamas won elections the previous year, but has been shunned by the West for refusing to renounce terrorism or follow the peace process.

Targets hit by Israel in Gaza included a university building, the Interior Ministry and the office of Ismail Haniya, the Hamas political leader. The Palestinian death toll reached 360, with at least 1,550 wounded, in just four days.

Most of the Palestinian victims have been Hamas security forces but at least 64 of them were civilians, according to UN figures. The toll includes two sisters, aged 4 and 11, who died in an airstrike on a rocket squad in northern Gaza this morning.

Four Israelis have been killed by Palestinian rockets since the Israeli attack was launched on Saturday.

“The goal of the operation is to topple Hamas,” Haim Ramon, the deputy to Ehud Olmert, the Prime Minister, said.

It was the first time since it launched its blistering offensive that Israel has openly stated that regime change is its ultimate goal. “We will stop firing immediately if someone takes the responsibility of this government, anyone but Hamas,” Mr Ramon said. “We are favourable to any other government to take the place of Hamas.”

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