The attack was done after dozens of Hamas militants broke out of the blockaded Gaza Strip and into nearby Israeli towns, killing hundreds and abducting others in an unprecedented operation.
Hamas said it had taken dozens of military and civilian hostages back to Gaza.
The surprise early morning attack — which was backed by a barrage of rockets fired from within Gaza — killed at least 250 people and wounded more than 1,500, according to Israel's national rescue service, during a major Jewish holiday on Saturday local time.