ALONG THE ISRAEL-GAZA BORDER — Israeli tanks and ground troops moved swiftly Sunday to seize large sections of Gaza, encircling its largest city and severing the narrow strip in two in what military commanders called a "real war" on the militant Islamic group Hamas.
On the first full day of Israeli ground operations following an eight-day air assault, Israeli infantry units, backed by Apache helicopters and Navy warships, swept into the Hamas-controlled coastal territory from east to west and took up positions in the former Israeli settlement of Netzarim, the closest to Gaza City, witnesses said.
As Gaza residents hunkered down in their homes for safety, heavy fighting and large airstrikes were seen in the northern towns of Gaza. Palestinian radio stations reported that northern hospitals were overwhelmed and that ambulances were unable to reach scores of people who were calling emergency numbers to report injuries.
Gaza medical officials said that 17 Palestinians were killed in the early hours of the offensive, which began Saturday night. More than 460 Palestinians have been killed since the Israeli air campaign began last Saturday, with about 2,500 others injured.
Israeli military officials said that 30 of their soldiers were injured, two severely.
"We do expect casualties," said Israeli Capt. Benjamin Rutland. "This is a real war."
The ground operation in densely populated Gaza carries huge risks for Israeli forces as they try to deal a crippling blow to Hamas's infrastructure and stop Palestinian militants from firing crude rockets from Gaza into Israel. On Saturday night, Israeli ground forces moved into northern Gaza in an attempt to seize control of open fields and orchards along the border that have been regularly used as rocket-launching pads.
But eight days of devastating Israeli bombardment have failed to stop the rocket fire. Another 30 rockets fell onto Israeli territory between midnight and 11 a.m. Sunday, according to Israeli Police spokesman Micky Rosenfeld. One rocket struck a house in Sderot, the southern Israeli town hardest hit by the attacks, although police officials reported no injuries.
Israeli military officials said their forces were exchanging fire with militants using mortars and remote-controlled bombs. In some parts of Gaza City, residents were forced to flee their homes when militants took up positions in apartment buildings.
The week-old confrontation has already devastated the Gaza Strip and pushed the 1.5 million residents into a new humanitarian crisis. Much of the territory has been thrown into darkness. Aid groups are unable to deliver food and supplies because of the ongoing fighting.
With the Israeli campaign moving into a new and more dangerous phase, it sets the stage for a deadly showdown that could significantly shake up Middle East political dynamics by either cowing hard-line Hamas ideologues into moderating their views or propelling the Israeli-Palestinian conflict into a deadly new spiral of unpredictable violence.
Hamas leaders in Syria have called for Palestinians to rise up and start a third uprising targeting Israel. Soon after Israeli tanks rolled into the Gaza Strip on Saturday night, Hamas leaders vowed to fight to the "last breath."
"We promise you that Gaza will be your graveyard," Hamas spokesman Ismail Radwan said on the Islamist group's Al Aqsa television station.
Speaking to his nation as soldiers advanced into Gaza, Israeli Defense Minister Ehud Barak said the military campaign "will not be short or easy."
"We are not war-hungry," said Barak. "But we shall not, I repeat we shall not -- allow a situation in which our towns, villages and civilians are constantly targeted by Hamas."
In an effort to isolate the Gaza Strip, Barak imposed a naval blockade on Saturday night and ordered thousands more reservists to report for duty.
The United Nations Security Council called an emergency session on Saturday evening in New York and Secretary General Ban Ki-moon urged an immediate halt to Israel's invasion. Ban said he'd conveyed his "extreme concern and disappointment" to Israeli Prime Minister Ehud Olmert.
The U.S. State Department, in a statement released Saturday evening, echoed Israel's stated goals.
"We are working toward a cease-fire that would not allow a reestablishment 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," it read in part. "It is obvious that cease-fire should take place as soon as possible, but we need a cease-fire that is durable, sustainable, and not time-limited."
At the same time, "we have expressed our concerns to the Israeli government that any military action needs to be mindful of the potential consequences to civilians," the statement concluded.
Before the invasion began, President George W. Bush, in his weekly radio address Saturday, backed Israel's use of force and said that Hamas must take the first step toward a cease-fire.
President-elect Barack Obama took no position. While Obama was "closely monitoring global events, including the situation in Gaza" according to his chief national security spokeswoman, Brooke Anderson, "There is one president at a time and we intend to respect that."
The Israeli ground operation is likely to quickly expand to Gazas southern border with Egypt as Israel tries to choke off the supply of weapons ferried into Palestinian militants by a network of smugglers tunnels.
Israel methodically destroyed hundreds of Gaza Strip targets, including the Palestinian Authority's Gaza Strip parliament building, government offices, the largest university, police stations, and mosques the Israeli military claimed were used to store rockets or hide militants.
Overnight Sunday, Israeli military officials said that air forces struck 45 Hamas targets and Navy ships fired on the headquarters of Hamas's intelligence office in Gaza City.
As part of the operation, the Israeli military has barred international reporters from entering Gaza, despite a court order directing them to let at least some journalists in to cover the unfolding conflict.
Television shots of the initial ground operations showed intense Israeli attacks. One strike along the Gaza coast created a massive fireball that lit up the night sky.
Israel's offensive came as tentative diplomatic efforts to bring the deadly conflict to a quick end failed to gather significant momentum over the weekend.
Several world leaders have called for an immediate truce, though Israeli leaders have said that they wont agree to a new deal with Hamas that is not enforced by outside monitors, perhaps from the United Nations, the Arab League or forces loyal to pragmatic Palestinian Authority President Mahmoud Abbas.
Israeli leaders rebuffed early appeals for a 48-hour truce and Hamas vowed to keep firing rockets until Israel re-opened its borders to allow critical food, aid and supplies into Gaza.
The perception that it's the aggressor plainly is hurting Israel. In Paris Saturday, more than 20,000 demonstrators marched, many chanting slogans like "Israel murderer!" In London, about 10,000 protestors chanted slogans such as "End the siege on Gaza" and "Stop the massacre!"
Both demonstrations — and others in other European capitals — preceded Israel's invasion.
Special correspondent Ahmed Abu Hamda contributed to this report from Gaza.