GAZA CITY, Gaza Strip — Israel carried out a blistering offensive of more than 50 air strikes in the Gaza Strip on Wednesday, assassinating Hamas’ military commander and targeting the armed group’s training facilities and rocket launchers in Israel’s most intense attack on the territory in nearly four years.

Israel said the air strikes, launched in response to days of rocket fire out of Hamas-ruled Gaza, were the beginning of a broader operation against the Islamic militants code-named “Pillar of Defense.”

Israeli defense officials said a ground operation was a strong possibility in the coming days, though they stressed no decisions had been made and much would depend on Hamas’ reaction. There were no immediate signs of extraordinary troop deployments along the border.

The attack came at a time when Israel seems to be under fire from all directions. Relations have been deteriorating with Egypt’s new Islamist government, Egypt’s lawless Sinai desert has become a staging ground for militant attacks on Israel, and the Syrian civil war has begun to spill over Israel’s northern border.

Earlier this week, Israel fired back at Syria – for the first time in nearly 40 years – after stray mortar fire landed in the Israeli-controlled Golan Heights.

With at least 10 Palestinians dead, including two young children, Wednesday’s offensive was certain to set off a new round of heavy fighting with Gaza militants, who have built up a formidable arsenal of rockets and missiles.

It also threatened to upset Israel’s relations with neighboring Egypt and shake up the campaign for Israeli elections in January. In a preliminary response, Egypt recalled its ambassador to Israel in protest.

In a nationwide address, Prime Minister Benjamin Netanyahu said Israel could no longer stand repeated attacks on its southern towns. Days of rocket fire have heavily disrupted life for some 1 million people in the region, canceling school and forcing residents to remain indoors.

“If there is a need, the military is prepared to expand the operation. We will continue to do everything to protect our citizens,” Netanyahu declared.

“We are at the beginning of the event, and not the end,” Defense Minister Ehud Barak said in a joint appearance with the prime minister. “In the long run, I believe the operation will help strengthen the power of deterrence and to return quiet to the south.”

In a sign that the operation was expected to broaden, the military was cleared to call up reserve units.

Residents in both Israel and Gaza braced for prolonged violence. Gazans rushed to stock up on food and fuel. After nightfall, streets were empty as the sounds of Israeli warplanes and explosions of air strikes could be heard in the distance.

Israel declared a state of emergency in its south and canceled school across the area for Thursday. Israeli police stepped up patrols around the country, fearing that Hamas could retaliate with bombing attacks far from the reaches of Gaza.

Hamas has in the past staged dozens of suicide bombings against Israelis and while its capabilities to do so today have been curtailed by Israeli and Palestinian crackdowns, it still has a network in the West Bank.

More than 65 rockets landed in southern Israel late Wednesday. One projectile struck a shopping mall in the southern city of Beersheba, causing heavy damage but no casualties, police said.

The Israeli military said 25 rockets were intercepted by the “Iron Dome” rocket-defense system.