Israel's prime minister is vowing to retaliate against the Islamist militant group Hamas following its surprise attack that killed at least 200 people.
More than 1,400 others have been treated for injuries.
Israeli Prime Minister Benjamin Netanyahu said, "The Israeli military will immediately use all its strength to destroy the capability of Hamas. We will strike them to their bitter end and retaliate on this black day they have brought upon Israel and its people."
Netanyahu said the war will take time, but that Israel will win.
Hamas launched the attack on Saturday morning. The militant group released a video of what it says was an attack on a border crossing checkpoint between Israel and Gaza. It's one of the Israeli military installations that was simultaneously targeted.
An unknown number of gunmen from the Gaza Strip breached border defenses and stormed into Israeli towns, randomly killing residents.
Israeli military officials say their troops continue to fight militants inside Israeli territory. They also said Hamas forces have captured soldiers and citizens.
Hamas military commander Mohammad Deif said, "We have decided to put an end to Israeli offensives so the enemy understands that they can no longer wreak havoc without being held accountable."
The size and nature of the attacks are unprecedented.
In addition to the cross border raids, the Israeli military says more than 3,000 rockets were launched from the Gaza Strip into southern Israel and other areas.
The Israeli air force is conducting raids against targets in the Gaza Strip. Health officials there say more than 230 people have died.
Two high-rise buildings hosting media outlets were destroyed by missile strikes. Officials say the sites were being used as a Hamas base of operations. They say they gave evacuation warnings to occupants before the buildings were struck.