Israeli forces fought fierce battles throughout Sunday to regain control of large swaths of the south after Hamas militants poured into Israel from Gaza and sought to reseal the border to prevent further incursions.
As the fighting raged, the Israeli government began evacuating civilians from towns and villages near the Palestinian enclave of Gaza, while trying to treat hundreds of wounded civilians, recover the bodies of the dead and determine how many Israelis were being held hostage.
Israel's cabinet approved the declaration of war after Prime Minister Benjamin Netanyahu announced the call-up of hundreds of thousands of reservists in a televised address on Saturday, saying "we are in a war and we will win it."
Hamas, which is backed by Iran, said it had sent additional personnel and weapons into Israel on Sunday and fired a new round of rockets from Gaza.
At the same time, Hezbollah, another Iranian-backed militant group, fired mortar shells and a missile at Israeli targets from southern Lebanon. The Hezbollah attacks signaled a possible second front in the conflict, as Israel prepares for a wider assault on military targets in Gaza. Hamas has sought to create more unrest, calling on Palestinians in the occupied West Bank to riot against Israeli soldiers there.
Smoke rises after an explosion at a bank following an Israeli air strike in Gaza.
Rubble fills the streets of Rafah in the southern Gaza Strip after an Israeli air strike.
On Sunday night, militants in Gaza again fired a barrage of rockets and Israel carried out airstrikes in the Palestinian territory. The Israeli military also said one of its Marine commandos had captured a deputy commander of Hamas's naval forces.
According to Israel's Army Radio, more than 700 Israelis have been confirmed dead and 2,408 wounded. According to the Palestinian Health Ministry, at least 413 Palestinians have been killed and some 2,300 injured in the Israeli counterattack on Gaza.
It is not clear how many of the Palestinian dead were militants, but the Israeli military says it has killed hundreds. Israeli military spokesman Jonathan Conricus said as many as 1,000 people crossed into Israel from Gaza on Saturday, including an unknown number dressed in civilian clothing.
More than 250 people have been found dead at the site of a music festival in southern Israel, state broadcaster Kan reported on Sunday, citing a volunteer search and rescue team. People at the festival said that on Saturday morning, gunmen opened fire on the crowd, sending people running for their lives. The participants also provided video footage of people running and squatting on the ground in the desert.
Israeli soldiers are struggling to dislodge Hamas militants from towns in the desert hinterland after a land, sea and air assault by the militant group caught Israel's security establishment by surprise. Hamas fighters initially pushed more than 20 miles inside Israel, and the militants entered at least four military bases along Israel's border with Gaza.
What happens in Israel, Hamas and the rest of the Middle East in the coming days will depend on the scale of Israel's military response and whether it opens another front with Palestinian militants in southern Lebanon or the West Bank, sparking a wider regional conflict.