Israeli tanks and troops have moved into southern Gaza. Warplanes have attacked three bridges and knocked out power to the coastal strip of 1.3 million people. The attacks are an attempt by the Jewish state to step up pressure on Palestinian militants holding a 19-year-old Israeli soldier captive.
No casualties were reported from the attacks.
It was Israel's first ground offensive since pulling its soldiers and settlers out of Gaza last summer. Israeli Prime Minister Ehud Olmert said Israel would not balk at "extreme action" to bring Cpl. Gilad Shalit, 19, home but did not intend to reoccupy Gaza.
Palestinian President Mahmoud Abbas deplored the incursion as a "crime against humanity," and a leading Hamas politician issued a call to arms against the Israeli troops.
The Associated Press contributed to this report.