Israeli Prime Minister Benjamin Netanyahu’s office says his Security Cabinet has declared the country at war following a deadly Hamas assault in southern Israel.

The decision, announced on Sunday, formally authorizes “the taking of significant military steps,” it said it a statement.

“The war that was forced on the State of Israel in a murderous terrorist assault from the Gaza Strip began at 06:00 yesterday,” it said.

It gave no further details. But Netanyahu had previous declared the country at war, and the military has promised a harsh response in Gaza.

Israeli media say at least 600 people have been killed in the surprise cross-border incursion by Hamas militants from the Gaza Strip.

Israeli soldiers battled Hamas fighters in the streets of southern Israel on Sunday and launched retaliation strikes that leveled buildings in Gaza, while in northern Israel a brief exchange of strikes with Lebanon’s Hezbollah militant group raised fears of a broader conflict.

There was still some fighting underway more than 24 hours after an unprecedented surprise attack from Gaza, in which Hamas militants, backed by a volley of thousands of rockets, broke through Israel’s security barrier and rampaged through nearby communities. At least 600 people have reportedly been killed in Israel — a staggering toll on a scale the country has not experienced in decades — and more than 300 have been killed in Gaza.

The militants also took captives back into the coastal Gaza enclave, including women, children and the elderly, who they will likely try to trade for thousands of Palestinian prisoners held by Israel.

The high death toll, multiple captives and slow response to the onslaught pointed to a major intelligence failure and undermined the long-held perception that Israel has eyes and ears everywhere in the small, densely populated territory it has controlled for decades.

Israeli Prime Minister Benjamin Netanyahu said the country was at war and would exact a heavy price from its enemies. Hamas leaders said they were prepared for further escalation.

A major question now was whether Israel will launch a ground assault into Gaza, a move that in the past has brought intensified casualties. Netanyahu vowed that Hamas “will pay an unprecedented price.” But, he warned, “This war will take time. It will be difficult.”

Civilians paid a staggering cost for the violence on both sides. Several Israeli media outlets, citing rescue service officials, said at least 600 people were killed in Israel, including 44 soldiers, while officials in Gaza said 313 people had died in the territory. Some 2,000 people have been wounded on each side. An Israeli official said security forces have killed 400 militants and captured dozens more.