Gaza/Tel Aviv  - After three days of massive airstrikes in the Gaza Strip, Israel was readying Monday to widen its offensive against Hamas by sending in ground forces.

The toll of Operation "Cast Lead" - launched Saturday to curb rocket and mortar attacks from the strip - meanwhile reached at least 345 Palestinian dead and 1,600 injured, Gaza emergency services chief Mu'awia Hassanein said. Two Israelis have also been killed and dozens injured.

Large columns of tanks, military vehicles and buses with Israeli soldiers on board meanwhile have moved southwards, deploying near the Israeli border with Gaza in what could indicate a possible impending ground invasion, witnesses said.

The Israeli army also declared the area around Gaza a "closed military zone," meaning no civilians will be allowed through roadblocks set up on key entry roads.

The Israeli cabinet on Sunday authorized the call up of 6,500 reserve soldiers. A military spokesman, Captain Benjamin Rutland, however, told Deutsche Presse-Agentur dpa the soldiers had not been mobilized yet and this could take half or up to one day.

Observers said this meant any ground offensive was unlikely to start Monday. They added Israel was likely to get as much out of the airstrikes as long as the clear wheather, forecast to turn Tuesday, permitted.

Israeli Defence Minister Ehud Barak reiterated Monday that the offensive in Gaza would be expanded "as much as necessary" until its goals were achieved.

Foreign Minister Tzipi Livni said Israel would "exhaust" the offensive until it achieved a change in the balance of power between itself and Hamas, the radical Islamic movement ruling Gaza.

The latest Palestinian deaths included at least seven killed in the northern Gaza Strip refugee camp of Jabaliya. An Israeli military spokeswoman said the target was a truck transporting "dozens" of Russian-type Grad rockets, which she said Hamas was apparently trying to relocate to another hideout as a result of Israel's massive assaults on warehouses and underground bunkers storing rockets.

A car in the southern Gaza Strip town of Khan Younis was also rocketed, killing four militants of the radical Islamic Jihad faction and one of the men's nine-year-old son.

In earlier airstrikes shortly before midnight, five daughters aged four to 15 of Anouar Balousha, a resident of the densely-populated Jabaliya camp, were killed when debris flew into his house, located close to a Hamas-used mosque targeted. Two boys aged around six and 12 were also killed by shrapnel in the southern town of Rafah, hospital officials said.

The Israel Air Force bombed and rocketed at least 65 more Hamas targets throughout Gaza Monday, bringing the total to more than 300.

Militant factions in Gaza, including Hamas and the Islamic Jihad, nevertheless continued their rocket and mortar attacks from the enclave at southern Israel, launching at least 50 by late Monday afternoon.

One Israeli, an Arab Bedouin from the south of the country, was killed Monday when a Russian-type Grad rocket fired by Hamas struck the construction site where he was working in the southern Israeli coastal city of Ashkelon. At least 14 others were injured.

The majority of the Palestinian dead are Hamas militants, but at least 57 are civilians, according to a "conservative" and "rising" tally carried out in hospitals by staff of a UN agency in Gaza, a spokesman, Chris Gunness, told .

The Gaza emergency services chief, Hassanein, said that more than 250 injured Palestinians were in serious condition and needed urgent transfers to hospitals outside the strip. Hamas, however, is said to have rejected an offer by Cairo to allow the transportation of severely wounded Gazans to Egypt.

A military spokeswoman in Tel Aviv said targets hit Monday included the Gaza City office of de-facto Palestinian prime minister Ismail Haniya, of Hamas. Residents said a neighbour's house in Gaza City's Beach refugee camp was hit instead.

Planes also bombed more smuggling tunnels along Gaza's southern border with Egypt, while the Israel Navy shelled Hamas outposts on the coast and inland, she said.

As many as 40 tunnels, used to smuggle goods and weapons into the strip, were said to have already been destroyed in a matter of minutes when bombed Sunday.

On Monday morning, a Palestinian stabbed and injured three Israelis in the West Bank settlement of Qiryat Sefer, west of Ramallah, a military spokeswoman in Tel Aviv said. An armed paramedic shot and seriously wounded the attacker.

Israeli police were on high alert to prevent further revenge attacks and rioting, after thousands of Arab Israelis and Palestinians, throwing stones and bottles, protested Sunday against the Gaza campaign in East Jerusalem and in such Arab towns as Umm el- Fahm, northern Israel.

Israel launched the Gaza offensive one week after a six-month, Egyptian-mediated truce ended, which Hamas had announced it would not renew. During that week, Gaza militants fired more than 200 rockets and mortars at southern Israel.(dpa)