Columns of Israeli military vehicles buttressing thousands of soldiers have entered the Gaza Strip, after artillery units and warplanes hammered the border area and attacked more Hamas targets Saturday.
As gun battles broke out between Israel's forces and Gaza's militants, Hamas warned that the densely-populated area would become a "graveyard" for Israeli soldiers.
Meanwhile, Israel's Defence Minister Ehud Barak told citizens to prepare for a prolonged battle.
"This will not be easy and it will not be short," he said during a television address, which aired shortly after the ground invasion began.
"We do not seek war but we will not abandon our citizens to the ongoing Hamas (rocket) attacks.
As the tanks and soldiers entered Gaza, the darkened sky was marked by massive fire balls and several major explosions could heard. The Israeli army has yet to release any information about casualties.
According to Israeli defence officials, 10,000 troops had gathered at the edge of Gaza, including tanks and special operations units.
The UN Security Council has called an emergency meeting for Saturday evening to discuss the crisis.
"We will do all that is necessary to provide a different reality for southern Israel, which has been under constant attacks for the past eight years," Foreign Minister Tzipi Livni told Channel 2 TV.
According to CTV's Middle East Bureau Chief Janis Mackey Frayer, the troops have entered the northern part of Gaza, backed by tanks and combat helicopters. She said they may attempt to secure an area along the border that is a known hotspot from which militants fire rockets.
"The buffer zone between Israel and Gaza at the border has been widened on the Gaza side," Mackey Frayer told Newsnet. "Every time the army has made it a little bit wider to push back the potential for these rocket squads to be able to fire rockets. So what they're going to try to do is contain at least part of this area."
She added that "the Israeli political establishment has been very clear in saying that they do not want to reoccupy the Gaza Strip."
"The objective they say is to seize some of the areas that Hamas has been firing rockets."
Mackey Frayer said that Hamas officials have taken to the airwaves claiming that they have killed Israeli troops but there has been no independent confirmation of the allegations.
The ground offensive was preceded by artillery fire directed at the northern town of Beit Lahiya, which may have been an attempt to clear local roads of any land mines or IEDs that Hamas militants may have planted in advance of an invasion by Israeli soldiers, Mackey Frayer said.
The artillery fire coincided with further air strikes Saturday, as planes dropped bombs on more than 40 Hamas targets. A mosque was also damaged, killing 10 people and injuring 33.
The conflict began on Dec. 27, with Israel saying it would no longer tolerate rocket attacks from Hamas on its border towns -- attacks that had intensified after the end of a truce agreement.
Leading up to the ground invasion, Israel dropped leaflets in downtown Gaza City to warn people to stay off the streets.
The strike on the mosque, which is located in Beit Lahiya, left seven of the injured in critical condition. Some reports have said children were at the mosque.
It is unclear if the dead are Hamas militants or civilians. According to The Associated Press, the mosque is named after a founder of Hamas who was killed by Israel in 2004.
After nightfall Saturday, an artillery shell also hit a house in Beit Lahiya and wounded a number of people.
According to Israeli officials who spoke on condition of anonymity, some army commanders are concerned the ground invasion could lead to heavy casualties, while others feel that the air offensive has already dealt Hamas a heavy blow.
Meanwhile, world leaders have called on both Israel and Hamas to agree to an internationally-monitored truce.
On Saturday, Israel targeted weapons storage facilities, training centres and the homes of two Hamas leaders.
The air strikes also struck the American International School, which is considered the most prestigious school in Gaza. The educational institution teaches an American curriculum in English, but is not connected to the U.S. government.
The strike destroyed the main building and killed a guard.
On Friday, Israel allowed nearly 300 Palestinians with foreign passports to flee the region.
Israeli troops entered the Gaza Strip after it appeared the latest air offensive had lost some steam, hitting more benign targets such as empty and abandoned buildings.
The offensive has caused considerable damage to Gaza's infrastructure. Air strikes have knocked out power and water in many areas, which has raised concerns of a pending humanitarian disaster.
Maxwell Gaylard, the UN humanitarian co-ordinator for the Palestinian Territories, said the offensive has wounded about 2,000 people in the last week.
"There is a critical emergency right now in the Gaza Strip," Gaylard told reporters.
Israel disputes this, but has increased the shipment of goods into Gaza.
French President Nicolas Sarkozy will visit the region this week, while U.S. President George Bush and UN head Ban Ki-moon have both come out in favour of an internationally monitored truce.
International pressure
Speaking at the United Nations in New York, Ban encouraged world leaders to step up efforts to establish a ceasefire that would be enforced by international monitors. He also suggested that an international force could offer protection to Palestinian civilians.
On Friday, Bush called the rocket attacks launched by Hamas an "act of terror" and said that a peace deal would have to include monitors to stop the smuggling of weapons into Gaza.
Palestinian President Mahmoud Abbas and several other Arab foreign ministers were scheduled to fly to New York this weekend to speak to the UN Security Council.
The group hopes the council will adopt an Arab draft resolution condemning Israel and demanding an end to the air strikes.
The U.S. has called the resolution, which should be debated by the council on Monday, "unacceptable" and "unbalanced" because it does not include a guarantee that Hamas will halt its rocket attacks against Israel.
The air strikes have killed more than 400 Palestinians, and 25 per cent of them may have been civilians, according to the UN. Four Israelis have also been killed by rocket attacks.
With files from The Associated Press
