Israeli airstrikes killed at least 15 Palestinians in the Hamas-controlled Gaza Strip and rocket fire wounded at least four Israelis as the worst violence in months escalated into a second day.
"The Israeli military will strike anyone who plans to hurt Israeli citizens," Defence Minister Ehud Barak said.
Gaza health officials reported 15 dead, all of them members of militant groups, and 25 wounded.
An Israeli army spokeswoman, speaking anonymously in accordance with regulations, said four Israelis were wounded, one seriously.
The latest round of bloodshed started with an Israeli air strike on a vehicle in Gaza yesterday that killed two Palestinians the army said were planning an attack from the Egyptian-controlled Sinai Peninsula. An attack from Sinai on the Israeli resort of Eilat killed eight in August.
The violence was the worst since that August attack and came just days after Israeli Prime Minister Benjamin Netanyahu returned from a trip to Canada and the US, where he said Israel must be free to protect itself from any threat