The Hamas movement has threatened to kill an Israeli hostage every time Israel bombs a Palestinian home without warning as Israel mobilised some 300,000 reservists and imposed a total blockade of the Gaza Strip, denying the enclave’s millions of residents access to food, water and fuel.

The warning from Hamas came on Monday as the death toll from the armed group’s surprise weekend attack climbed to 900 in Israel and revenge attacks by Israeli forces on the besieged Gaza Strip killed more than 700 people and left some 3,700 others wounded.

Residential apartment blocks, hospitals, schools and a mosque have been among the sites attacked by Israeli fighter jets, artillery and drones, according to media reports and witnesses.

Hamas spokesperson Abu Ubaida issued the threat to kill Israelis from the dozens held captive by the armed group. He said an Israeli hostage would be killed for every Israeli bombing of a civilian house without warning.

Israeli Foreign Minister Eli Cohen said more than 100 people were taken captive by Hamas during the deadly cross-border incursion over the weekend.

As Israeli forces conducted intense retaliatory attacks on Gaza on Monday, Israel’s Defence Minister Yoav Gallant drew international condemnation by announcing a total blockade of the densely populated and besieged enclave, which is home to 2.3 million people.

Gallant said Israel would impose a “complete siege” on Gaza. “No electricity, no food, no water, no gas – it’s all closed.”

United Nations Secretary-General Antonio Guterres said he was “deeply distressed” by the siege announcement and warned that Gaza’s already dire humanitarian situation will now “only deteriorate exponentially”.

Guterres also said some 137,000 people were taking shelter with the UN Relief and Works Agency for Palestinian Refugees (UNRWA) at schools across Gaza.

UNRWA said on Tuesday that almost 190,000 people have been displaced in Gaza amid the Israeli attacks and the figure is expected to grow further as the violence intensifies.

Nearly half a million people have also not received food rations this week in Gaza as UN food distribution centres have been forced to remain closed amid the Israeli onslaught, UNRWA said.

Human Rights Watch said Israel’s total blockade on the necessities of life for everyday people in Gaza was a war crime.

“Defense Minister Gallant’s statements are abhorrent,” Omar Shakir, Israel and Palestine director at Human Rights Watch, said in a statement.

“Depriving the population in an occupied territory of food and electricity is collective punishment, which is a war crime, as is using starvation as a weapon of war. The International Criminal Court should take note of this call to commit a war crime,” he said.

Abhorrent. This is a call to commit a war crime by @yoavgallant. The @IntlCrimCourt should take note.

Quote by @OmarSShakir ⤵️ https://t.co/kKVo6YtpI1 pic.twitter.com/neHQMwnXVn

— Human Rights Watch (@hrw) October 9, 2023

Shakir also condemned the threat by Hamas to kill hostages, warning that such action was also a war crime.

“All hostages should be safely released to their families,” he said.

Grotesque. These threatened acts would amount to flagrant war crimes by Hamas’ armed wing. The @IntlCrimCourt will be watching.

Quote from @OmarSShakir ⤵️ https://t.co/FuNtvHe0YG pic.twitter.com/6cnHODLWyZ

— Human Rights Watch (@hrw) October 9, 2023

On the diplomatic front, Egyptian President Abdel Fattah el-Sisi and his Turkish counterpart Recep Tayyip Erdogan called on Hamas and Israel to immediately end violence and protect civilians, the Egyptian presidency said.

Erdogan urged Israel against “indiscriminately” attacking civilians and delivered measured criticism of Hamas, urging both sides to respect the “ethics” of war.

The United Kingdom, French, German, Italian and US governments issued a joint statement on Monday recognising the “legitimate aspirations” of the Palestinian people and supporting equal measures of justice and freedom for Israelis and Palestinians alike.

They said they would remain “united and coordinated” to ensure Israel can defend itself.

But the prospect that fighting could spread also alarmed the region and the world.

Lebanese armed group Hezbollah fired rockets into northern Israel in response to at least three of its members being killed in Israeli shelling of Lebanon.

Israel said one of its deputy commanders was also killed in an earlier cross-border raid from Lebanon.