Israel stepped up its land offensive in Gaza with artillery, tanks and gunboats on Friday and declared it could "significantly widen" an operation Palestinian officials said was killing ever greater numbers of civilians.
Israeli gunboats lit up the sky with their fire before dawn while helicopters fired into the coastal enclave. Hamas fired mortar rounds at the invading troops and rockets across the border at the southern Israeli towns of Ashdod and Ashkelon.
Palestinian health officials said 27 Palestinians, including a baby, two children and a 70-year-old woman, had been killed sinceIsrael poured ground forces into the densely-populated strip of 1.8 million Palestinians on Thursday.
The action followed 10 days of barrages against Gaza from air and sea and hundreds of rockets fired by Hamas into Israel.
"We chose to start this operation after we exhausted other options and reached the conclusion that without it we could pay a much higher price," Israeli Prime Minister Benjamin Netanyahu told reporters before a special cabinet session at Tel Aviv military headquarters. "The main goal is to restore quiet."
"My instructions...to the Israeli army, with the approval of the security cabinet, is to prepare for the possibility of a widening, a significant widening of the ground operation."
He did not say what form a widened operation might take. Israel says its forces have focused so far on seeking out tunnels Palestinian militants might use for cross-border raids.
One such infiltration was narrowly thwarted on Thursday, with the army saying it had repelled 13 Hamas gunmen after they emerged from a tunnel close to an Israeli farming community.
To back up regular forces, Israel said it was calling up 18,000 military reservists, adding to 30,000 already mobilised
Hamas spokesman Sami Abu Zuhri responded with defiance to the Israeli escalation, saying: "Netanyahu is killing our children and will pay the price. The ground invasion doesn't frighten us and the occupation army will sink in Gaza's mud."
Hamas wants Israel and Egypt, whose military-backed government is at odds with the Palestinian Islamists, to lift border restrictions that have deepened Gaza's economic hardship and unemployment.
Israel said one of its soldiers was killed and several others wounded in Gaza clashes overnight. Hamas said its men were shelling the tanks with mortars and setting off bombs against troops crossing the sandy frontier under smokescreens.
In all, 258 Palestinians, most of them civilians, have been killed since the fighting began on July 8, Gaza officials said.
Dozens of Palestinian families, forewarned by evacuation notices Israel had disseminated with leaflet drops and automated phone messages, fled toward the interior, leaving empty streets.
Infra-red video released by the military showed six tanks rolling into Gaza by night, followed by two long infantry columns, after a soldier opened a gate in the border fence.
"We are using a very high level of firepower and artillery," military spokesman Brigadier General Motti Almoz said. "A great number of soldiers are in action in the Gaza Strip, soldiers are overtaking their targets, tunnels, Hamas targets," Almoz said, and several "points of friction" with gunmen.
Among Friday's fatalities were three teenage brothers, who medics said were shelled by an Israeli tank inside their house, at a residential building in Beit Lahiya, a northern town.
Though they are die-hard foes, Israel says it does not intend to topple Hamas, the dominant Islamist force in Gaza.
Live television showed rockets shot down by Israel's Iron Dome interceptor. No casualties were reported from the salvoes.
Israeli media said the army appeared to be probing northern and southern frontier zones for cross-border tunnels, Palestinian command bunkers and buried rocket silos.
The soldier was Israel's second fatality in eleven days of fighting. A rocket attack killed a civilian two days ago.
Lieutenant-Colonel Peter Lerner, another military spokesman, said Israel had killed 14 Palestinian gunmen in "exchanges of fire throughout Gaza" and destroyed 20 rocket launchers.
Hamas said its fighters had repelled Israeli forces in the northern Gaza town of Beit Hanoun, wounding seven soldiers.
Among sites targeted by Israeli forces in Gaza on Friday was the Al-Jawhara building housing various media outlets, medics and witnesses said. One journalist was wounded.
Israel calls the Gaza offensive a response to mounting rocket salvoes, more than 100 a day, fired by the Palestinians into its cities, sending hundreds of thousands of Israelis dashing to shelters as far north as the Tel Aviv business hub.
Hostilities were stoked by the killing of three Israeli teens in the occupied West Bank last month and the death on July 2 of a Palestinian youth in a suspected revenge murder. Israel briefly held fire on Tuesday after Egypt, which also borders Gaza, announced a truce plan; but Hamas and other militants balked saying their conditions had not been addressed.
The fighting has been the worst between Israel and Palestinians in two years. The United Nations Security Council will meet on Friday to discuss the developments.
The U.N. Secretary-General Ban Ki-moon, speaking after the announcement of the ground assault, implored Israel to do more to stop Palestinian civilian deaths.
Fighting resumed immediately after the end of a five-hour humanitarian truce on Thursday requested by the United Nations to allow Palestinians to stock up on food.
"Israel had agreed to the Egyptian proposal for a ceasefire and to the United Nations' proposal for a humanitarian truce. In both cases Hamas continuing firing," Netanyahu said.
Hamas leaders have talked up their "tunnel campaign" against Israel. One publicity video showed Palestinian fighters hauling rockets through a narrow passage to load onto a launcher that appears buried in an orchard. It is then fired remotely after its mechanised cover slides open.
Israel last mounted a large-scale invasion of the Gaza Strip during a three-week war in late 2008 and early 2009 that claimed 1,400 Palestinian and 13 Israeli lives. More»