Hamas has declared that it will kill one person who was captured in Israel for every airstrike sent into Gaza.
The Palestine Hamas group has threatened to kill one hostage for every unannounced Israeli air strike in civilian areas of the Gaza Strip, in a dramatic escalation.
The terror group claimed it would film and broadcast the killings if Israel did not provide advance warning of bombings.
The threat came hours after Israel’s air force hammered Gaza with bombs and missiles in retaliation for the killing of 800 people, mostly civilians, in Israel at the weekend.
The number of Palestinians killed in Gaza rose to more than 680.
Around 700 people, including 73 soldiers, have been killed in Israel since the attack was launched on Saturday morning.
“We have decided to put an end to this and as of now we declare that any targeting of our people in their homes, without prior warning, will be regrettably faced with the execution of one the hostages of civilians we are holding,” said Hamas spokesman Abu Obeida.
Hamas issued the threat as speculation builds that Prime Minister Benjamin Netanyahu will mount a full-scale invasion of Gaza in the coming days.
It is unclear whether the threat would have any effect on Israeli plans.
Israeli officials earlier told The National that any negotiations with Hamas were off the table.
Israel has used a controversial “roof-knocking policy” in Gaza, which it says warns civilians of incoming air strikes.
But Israeli media has reported that the army is not currently using this method, in which non-explosive missiles are dropped on the roof of a building before it is bombed, or text messages sent to building residents.
Tzipi Livni, a former foreign minister in Ariel Sharon and Ehud Olmert’s cabinets, told CNN that the execution threat means Israel’s government is now “facing really difficult decisions”.
She urged countries that support Hamas to urge it to step back from the brink.
“I know Hamas doesn’t care about the international community but they do care about the countries that support them,” said Ms Livni, who was in opposition to Netanyahu’s previous administration.
She urged the terror group to de-escalate and release hostages, but repeated that Israel believes “it’s time that Hamas will pay the ultimate price”.
Speaking earlier, Israeli President Isaac Herzog said that Hamas had mirrored ISIS.
“Hamas has imported, adopted, and replicated the savagery of ISIS,” he said.
“Entering civilian homes on a holy day and murdering in cold blood whole families. Young and old. Violating and burning bodies.
“Beating and torturing their innocent victims – Jews and Muslims and other faiths. The brutality. The inhumanity. The barbarity of monsters – not humans, monsters.”
With as many as 100 hostages taken from Israel, the Netanyahu government is under huge pressure to rescue them.
Families have been highly critical of how long it took police and military to reach the southern towns attacked by Hamas, and about the lack of information since Saturday.
“We don’t know anything, we just sit in front of the TV all day, waiting to hear something about my sister,” the relative of one missing woman told Israel’s i24 channel.
“The last we heard from her was on Saturday morning. She said something was going to happen to her, and she started screaming.”
She said her sister attended the Nova music festival, where more than 200 people were killed.