The military used overwhelming firepower from tanks, artillery and aircraft to protect the advancing soldiers, and Gaza officials said at least 31 civilians were killed in the onslaught. The military said troops killed several dozen militants, but Gaza officials could confirm only four dead — in part because rescue teams could not reach the battle zones. One Israeli soldier was killed.

The ground invasion and live images of the fighting in Gaza drew international condemnations and dominated news coverage on Arab satellite TV stations, many of which aired footage of wounded Palestinians at hospitals. Hamas threatened to turn Gaza into an Israeli "graveyard."

Thousands of soldiers in three brigade-size formations pushed into Gaza after nightfall Saturday, beginning a long-awaited ground offensive against the area's Hamas rulers after a week of intense aerial bombardment. Black smoke billowed over Gaza City at first light as bursts of machine gun fire rang out.

The ground operation is the second phase in an offensive that began as a weeklong aerial onslaught aimed at halting Hamas rocket fire that has reached deeper and deeper into Israel, threatening major cities and one-eighth of Israel's population.

The new deaths brought the death toll in the Gaza Strip to more than 500 since Dec. 27. Palestinian and U.N. officials say at least 100 civilians are among the dead.