The rubble of a mosque in Gaza, destroyed in an Israeli airstrike.
Israel's vow to reduce Hamas sites in Gaza to "rubble" has raised concern in the UN. Secretary-General Antonio Guterres said military operations "must be conducted in strict accordance with international humanitarian law".
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"While I recognize Israel's legitimate security concerns, I also remind Israel that military operations must be conducted in strict accordance with international humanitarian law," said UN Secretary-General Antonio Guterres.
Hamas, meanwhile, has threatened to kill hostages if the Israeli army carried out air strikes without prior warning targeting residents of the Gaza Strip.
"Every targeting of our people without warning will be met with the execution of one of the civilian hostages," said Ezzedine al-Qassem Brigades, the armed wing of Hamas.
Over the last three days, Israel has counted over 800 dead. Palestinian officials said Israel's barrage of air strikes on Gaza has raised the death count to 687. The US has confirmed that nine of its citizens have died. rael's army said it has regained control of southern areas near the Gaza Strip taken over by the Hamas.
Defence Minister Yoav Gallant said Israel would impose a "complete siege" on the long-blockaded enclave. The impact on its 2.3 million people will be "No electricity, no food, no water, no gas -- it's all closed", he said.
Palestinians in the impoverished and crowded coastal territory are bracing for an Israeli ground attack aiming to defeat Hamas and liberate at least 100 hostages.
On Day 3 of the war, skies over Gaza were blackened by plumes of smoke as fighter jets roared above. Hamas kept firing rockets as far as Jerusalem, where air raid sirens blared and detonations were heard.
"Overnight IDF fighter jets, helicopters, aircraft and artillery struck over 500 Hamas and Islamic Jihad terrorist targets in the Gaza Strip," said a statement by the Israeli Defense Forces.
Israel Prime Minister Benjamin Netanyahu has warned Gaza civilians to get away from all Hamas sites which he has vowed to turn "to rubble".
On Saturday, more than 1,000 Hamas troops broke through the border fence in Gaza and swarmed to nearby Jewish communities. There gunmen went house to house, mowing down people or abducting them back into Gaza.
