Israel declares war and approves 'significant' steps to retaliate for surprise attack by Hamas

The Israeli government formally declared war Sunday and gave the green light for 'significant military steps' to retaliate against Hamas for its surprise attack from the Gaza Strip, portending greater fighting ahead as the toll from the conflict passed 900 dead and thousands wounded on both sides.

The Israeli government formally declared war Sunday and gave the green light for "significant military steps" to retaliate against Hamas for its surprise attack from the Gaza Strip, portending greater fighting ahead as the toll from the conflict passed 900 dead and thousands wounded on both sides.

More than 24 hours after Hamas launched its unprecedented incursion out of Gaza, Israeli forces were still trying to crush the last groups of militant fighters holed up in several towns of southern Israel. 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 as Israeli airstrikes pound the territory.

Authorities were still trying to determine how many civilians and soldiers were seized by Hamas fighters during the mayhem and taken back to Gaza. From videos and witnesses, the captives are known to include women, children, and the elderly.

As many as 1,000 Hamas fighters were involved in the assault, U.S. Secretary of State Antony Blinken said on ABC's "This Week" -- a high figure that underscored the extent of planning by the militant group ruling Gaza. The gunmen rampaged for hours, firing on civilians in towns, along highways and at a techno music festival being held in the desert near Gaza.

Civilians on both sides were already paying a high price.

A line of Israelis snaked outside a central Israel police station to supply DNA samples and other means that could help identify missing family members. Israeli TV news aired a stream of accounts from relatives of captive or missing Israelis who wept and begged for assistance and information.

In Gaza, the tiny enclave of 2.3 million people sealed off by an Israeli-Egyptian blockade for 16 years since the Hamas takeover, residents feared an intensified onslaught. Israeli strikes flattened a number of residential buildings. More than 20,000 people who fled their homes crowded into schools run by the U.N. agency for Palestinian refugees, UNWRA, the agency said.