The bodies of about 1,500 militants have now been found on Israeli territory after Saturday’s surprise attack, according to the country’s military.
Israel says more than 150 of its civilians and soldiers were kidnapped and are being held hostage in Gaza.
Israel-Gaza latest: Israel warns its offensive ‘won’t be clean’
Harrowing tales have emerged of families being taken away, with relatives left with no clue about their fate.
Hamas has warned it will kill a hostage every time Israel launches a retaliatory air strike without a pre-warning to enable civilians to reach safety.
Some 770 Palestinians have died in the Gaza Strip and 4,000 injured in strikes so far, say Palestinian health authorities.
In retaliation, Israel has announced a siege of Gaza, cutting off food, power and water as it hits back at Hamas targets in the thin coastal strip.
A huge number of Israeli tanks are also gathered at the border ahead of an expected ground assault, with Israel’s prime minister promising devastating revenge.
The Israel Defence Force (IDF) says 300,000 Israeli soldiers have been mobilised over the last 48 hours, with 35 battalions being organised into four divisions.
Israel will respond in Gaza “very aggressively. This is a game changer”, the IDF added.
The country’s air force, meanwhile, said it is launching an “extensive attack against terror targets” in the Gaza Strip.
Some 900 Israelis were killed in the Hamas attack – which Israeli officials have likened to its own 9/11 or Pearl Harbour.
That number includes about 250 festival-goers slaughtered by gunmen who prowled the site shooting them dead for hours.
One couple have told Sky News how they managed to escape the massacre by driving across a field.
