Gaza/Tel Aviv - Israel rejected calls by the UN, EU and France for a ceasefire and instead prepared for what could be "long weeks of combat," as a ferocious air offensive against Hamas in he Gaza Strip entered its fourth day Tuesday.

An Israeli defence official said French Foreign Minister Bernard Kouchner had proposed to Israel that it unilaterally halt its assault for 48 hours to give Hamas a chance to end its rocket and mortar attacks as well.

Kouchner had submitted the proposal to Israeli Defence Minister Ehud Barak, who had passed it on the caretaker Prime Minister Ehud Olmert, the official, who spoke on condition of anonymity because of the sensitivity of the information, told Deutsche Presse-Agentur dpa.

But Olmert's spokesman, Mark Regev, said that although Israel would work "energetically" with foreign governments and international organizations to allow a "constant flow" of aid into the strip, it would not suspend its offensive before its goals were achieved.

"Giving Hamas a rest period to re-group and rearm, reducing the pressure on that organization, would be a mistake," he told dpa.

Olmert himself earlier said the air campaign, which has seen close to 400 airstrikes on Hamas targets in Gaza in just four days, was only the "first" of a "series" of phases of the offensive.

Ground troups have massed outside Gaza since Sunday, but have yet to enter.

At least 18 people died in Tuesday's airstrikes, bringing the the total number of Palestinian killed since Operation "Cast Lead" started Saturday to 380, the highest toll by far in decades of Israeli-Palestinian fighting.

More than 1,800 have been injured, Gaza emergency services chief Mo'aweia Hassanein said.

Four Israelis, including two Arabs - a Druze soldier and a Bedouin construction worker - have also been killed and dozens injured in rocket and mortar attacks.

Israeli fighter jets flew another sortie over the southern Gaza Strip's border with Egypt around sunset Tuesday, bombing a series of smuggling tunnels, military officials said.

Already on Sunday, as many as 40 tunnels were destroyed in a matter of minutes, when as many planes nearly simultaneously dropped heavy bombs on each of them. The vast network of tunnels under the border town of Rafah is used to smuggle both weapons and scarce goods into the enclave, circumventing a tight Israeli blockade.

Egypt had closed the Rafah border crossing, through which some 100 seriously injured patients had been transferred since late Sunday, shortly before the sortie late Monday - a clue that Israel may have given Cairo prior notice.

Regev, responding to a question by dpa whether Israel was willing to accept an immediate new truce, had already said earlier in the day that it wanted no "instant fix" that would only temporarily end rocket and mortar attacks from the strip.

The Israeli official was unable to say how long the offensive may take, but noted that achieving its objectives "may take time."

Deputy Defence Minister Matan Vilnai, said Israel was prepared for "long weeks of combat." Hamas, Vilnai told Israel Radio, still had several hundreds of rockets.

Barak earlier said the objectives were not only curbing rocket and mortar attacks from Gaza against southern Israel, but also dealing a "forceful blow" to Hamas and "fundamentally changing the situation in Gaza."

Hamas said it was unfazed. The onslaught against it only made it "more determined to respond," spokesman Fawzi Barhoum said.

He warned that Israel would not succeed in toppling the Hamas regime in Gaza, pointing out that its 2006 war with Hezbollah had only strengthened the Lebanese radical Shiite movement.

Barhoum condemned the current Israeli air campaign as "genocide."

Most of the dead were members of Hamas' security forces and armed forces, but according to UN officials, at least 62 were women and children. They said they did not know how many of the men killed were civilians.

The latest civilian deaths included two sisters, aged 4 and 11. Initial reports said they had been riding a donkey cart struck by an Israeli missile, while later reports said they were taken to hospital on the donkey cart, but in fact killed and fatally injured by shrapnel as they took out the garbage and a missile hit a nearby building of a militant faction, the PFLP.

Hamas' Gaza City government headquarters, housing several ministries and the office of de-facto prime minister Ismail Haniya, was also again among the targets hit Tuesday, reducing parts of it to rubble.

A defiant Hamas deepened its rocket attacks into Israel Tuesday and late Monday, for the first time ever reaching Israeli communities within a range of 30 kilometres from the strip and slightly beyond, including the coastal town of Ashdod and the Bedouin town of Rahat, nor far from Beersheba, the fourth largest city in Israel where rocket alarms sounded for the first time ever Tuesday.

Two Israelis were killed late Monday, including an Ashdod woman unversed in how to take cover who fled her car to hide in a bus stop, which was later punctured with shrapnel.

Israel launched the offensive one week after a fragile, six-month truce mediated by Egypt expired on December 19 and Hamas announced it would not extend it under the same terms. During that week, Hamas as well as the Islamic Jihad and other militant factions launched more than 180 rockets into southern Israel.

Both the UN and Brussels, in separate statements, called for an immediate end to hostilities, and the UN under secretary general for humanitarian affairs accused Israel of using "excessive force." (dpa)