Israeli soldiers advance near the border with central Gaza during a ground operation by the Israeli army late January 3, 2009. Israeli troops clashed with Hamas fighters as they advanced into Gaza on Saturday in the first ground action of an eight-day offensive on the Palestinian enclave, a witness and the Israeli army said. REUTERS/Baz Ratner

A column of tanks entered the besieged territory though the Beit Hanoun crossing shortly after nightfall on Saturday, as the Israeli cabinet said it had called up about 9,000 reservists as part of its preparations.

Hamas has vowed to defeat the Israeli army following the invasion.

Reuters news agency said a senior Hamas official has said that its fighters had killed a number of Israeli soldiers but there was no word from Israel on any casualties.

Two Israeli children hold banners during a left-wing protest in Tel Aviv against Israel's offensive in Gaza January 3, 2009. Israeli troops clashed with Hamas fighters as they advanced into Gaza on Saturday in the first ground action of an eight-day offensive on the Palestinian enclave, a witness and the Israeli army said. REUTERS/Eliana Aponte

Reservists mobilized

Ehud Barak, Israel's defense minister, said: "Our aim is to force Hamas to stop its hostile activities against Israel and bring about significant change.

"We have carefully weighed all our options, we are not war hungry but we should not allow a situation where our towns are constantly targeted by Hamas.

"The ground operation includes endangering the lives of the forces. I know that there are risks. It will not be easy or short, but we are determined. Now is the time to do what needs to be done".

Ayman Mohyeldin, Al Jazeera's correspondent in Gaza, said: "Residents in the Beit Hanoun area say they have seen the movement of tanks into the territory.

"There is absolute fear and terror, it is pitch black, power lines have been cut throughout the strip, more than 250,000 people in northern Gaza are without electricity.

"The biggest concern is a ground invasion could result in urban warfare.

James Denselow, a Middle East specialist from Kings College, London, said "Hamas operates as an asymmetrical force. It knows its strength and knows indiscriminate rockets can cause alarm.

"This is why the Israeli army has used air strikes to 'soften' the ground followed by an assault at night when low-tech armies such as Hamas find it very hard to fight."

The ground assault came as the death toll of Palestinians climbed past 450 on Saturday as a strike on a northern Gaza town killed at least 11 people, including one child, who were praying in a mosque.

Israeli artillery started firing shells into the Gaza Strip for the first time on Saturday, ahead of the ground offensive.

Ofir Gendelman, an Israeli foreign ministry spokesman, said: "All we asking for is to create a normal life for people of Israel. We'll keep on targeting Hamas objectives until the situation on the ground there is transformed.

"They [Israeli ground forces] will be completing the mission of the air force, going for Hamas headquarters and weapons caches and giving a blow to their capability to launch attacks into Israel.

"It will take quite a number of days to get the job done."

"If you commit the stupidity of launching a ground offensive, then a black destiny awaits you," Khaled Meshaal, the political leader of Hamas, said on Friday.

"You will soon find out that Gaza is the wrath of God."

Meshaal, speaking from the Syrian capital of Damascus on Friday, said Palestinians in Gaza were ready for any land offensive made by the Israelis.

"This battle was imposed on us and we are confident we will achieve victory because we have made our preparations.

"Our position is clear. We will not give in. Our resolve cannot be broken," he said.

"Our demand is also clear. The war must end, the siege lifted, and crossing points open without restriction."

-AlJazeera