Thousands of Israeli troops backed by columns of tanks and helicopter gunships launched a ground offensive in Gaza on Saturday night, with officials saying they expected a lengthy fight in the densely populated territory after eight days of punishing airstrikes failed to halt militant rocket attacks on Israel.
Israeli defense officials told FOX News that an estimated 30 Hamas militants had been killed in the incursion so far, though precise numbers are hard to pin down.
Israeli leaders said the operation, known as Cast Lead, was meant to quell militant rocket and mortar fire on southern Israel.
The United Nations, meanwhile, scheduled emergency consultations Saturday night on the escalation, but the United States blocked approval of a statement calling for an immediate cease-fire in the Gaza Strip and southern Israel.
"We are not war hungry, but we shall not ... allow a situation where our towns, villages and civilians are constantly targeted by Hamas," Defense Minister Ehud Barak said. "It will not be easy or short, but we are determined."
Barak described Israel as "peace seekers."
"We have restrained ourselves for a long time but now is the time to do what needs to be done," he said.
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Israel launched its aerial campaign a week ago in a bid to halt weeks of intensifying Palestinian rocket fire from Gaza. That offensive dealt a heavy blow to Hamas but failed to halt the rocket fire.
Hamas, whose charter calls for the destruction of Israel, responded to the new offensive by saying Gaza would become a "graveyard" for Israeli troops.
The fighting in Gaza has created "increased chatter" on radical Web sites and in the intelligence community during the past 48 to 72 hours, sources tell FOX News.
Although they were quick to say there have been no specific or credible threats, the escalation in the Middle East, "can be seen by our enemies as an opportunity" to attack U.S. and Israeli interests outside of the region, sources told FOX.
Historically, Hamas and Al Qeada do not have an operational relationship, but their call to hit Israeli targets outside the region could inspire a "lone wolf" attack, sources said.
Israeli airstrikes in the Gaza Strip had intensified Saturday evening, setting the stage for the incursion that comes despite international efforts to secure a cease-fire and avert a ground war between Israel and Hamas.
"We are working toward a cease-fire that would not allow a re-establishment of the status quo ante, where Hamas can continue to launch rockets out of Gaza and to condemn the people of Gaza to a life of misery," U.S. State Department spokesman Sean McCormack said in a written statement issued Saturday evening.
McCormack added that a cease-fire should come "as soon as possible," but it should be "durable, sustainable and not time-limited."
Israeli Welfare Minister Isaac Herzog, in an interview with FOX News, said the aim of the ground offensive "is to make a dramatic change in the circumstances on the ground, whereby Israeli citizens on our side of the border will be able to resume living normally."
"Right now we've started a ground operation, which is aimed at preventing missile launchings against Israel from various sites in Gaza Strip," Herzog said. "It may take time Hamas will try to show in their arrogant way that they are still around, and our aim is to protect our citizens like any normal society would do."
Gaza residents said troops were seen before dawn Sunday in the town of Beit Lahiya, north of Gaza City, and the sound of intense fighting could be heard just east of the city, toward the border with Israel.
In the city itself, the Hamas-run Al Aqsa radio station was in flames from a missile strike. Staff had evacuated the building about a week earlier, at the start of the Israeli offensive, and continued broadcasting from another location.
Into the night Saturday, heavy Israeli artillery fire hit east of Gaza City, in locations were Hamas fighters were deployed. The artillery shells were apparently intended to detonate Hamas explosive devices and mines planted along the border area before troops marched in.
Gun battles could be heard, as troops crossed the border into Gaza. Local TV networks broadcast images of troops marching single file. The troops were also backed by helicopter gunships.
Israeli security officials have said the ground offensive could last several days, but that the objective is not to reoccupy Gaza.
An SMS message sent by Hamas' military wing, Izzedine al-Qassam, said that "the Zionists started approaching the trap which our fighters prepared for them."
French President Nicolas Sarkozy is visiting the region next week, and U.S. President Bush and U.N. chief Ban Ki-moon both spoke in favor of an internationally monitored truce.
The U.N. chief has urged key world leaders to intensify efforts to achieve an immediate Israeli-Hamas cease-fire that includes international monitors to enforce a truce and possibly to protect Palestinian civilians.
Palestinian President Mahmoud Abbas and several Arab foreign ministers are flying to New York over the weekend to urge the Security Council to adopt an Arab draft resolution that would condemn Israel and demand a halt to its bombing campaign in Gaza.
From 2001 through May 2008, Hamas launched more than 3,000 Qassam rockets and 2,500 mortar attacks against Israeli targets, and on Friday, exiled Hamas leader Khaled Meshaal said from Damascus that his group was prepared for an invasion and may attempt to abduct soldiers, as it has in the past.
Israel launched the new round of airstrikes on Gaza in response to renewed missile attacks by Hamas after the two sides' six-month cease-fire ended last month.
FOX News' Mike Tobin and the Associated Press contributed to this report.