The Israeli government formally declared war Sunday afternoon and gave the green light for "significant military steps" to fight the Palestinian resistance group Hamas.

More than 24 hours after an unprecedented surprise attack out of Gaza, Israeli forces were still fighting Hamas members in several towns.

At least 700 people have reportedly been killed in Israel while more than 300 have been killed in Gaza as Israeli airstrikes pounded the territory.

The declaration of war portended greater fighting ahead and a major question was whether Israel would launch a ground assault into Gaza, a move that in the past has brought intensified casualties.

Meanwhile, in northern Israel, a brief exchange of strikes with Lebanon's Hezbollah fanned fears that the fighting could expand into a wider regional war.

The declaration of war announced by Israel’s Security Cabinet was largely symbolic, said Yohanan Plesner, the head of the Israel Democracy Institute, a local think tank. But it "demonstrates that the government thinks we are entering a more lengthy, intense and significant period of war."

Israel has carried out major military campaigns over the past four decades in Lebanon and Gaza that it portrayed as wars but without a formal declaration.

The Security Cabinet also approved "significant military steps." The steps were not defined, but the declaration appears to give the military and Prime Minister Benjamin Netanyahu a wide mandate.

Speaking on national television Saturday, Netanyahu vowed that Hamas "will pay an unprecedented price." He further warned: "This war will take time. It will be difficult."

Hamas said the assault, named "Operation Al-Aqsa Storm," was in response to the 16-year blockade of Gaza, the Israeli occupation and a series of recent incidents that have brought Israeli-Palestinian tensions to a fever pitch.

Over the past year, Israel’s far-right government has ramped up settlement construction in the occupied West Bank. Israeli settler violence has displaced hundreds of Palestinians there, and tensions have flared around the Al-Aqsa mosque, a flashpoint site in East Jerusalem.