Israeli Prime Minister Benjamin Netanyahu faces mounting international and domestic pressure after the killing in Gaza of six captives, with US President Joe Biden saying he is not doing enough to secure the release of hostages.
Britain said Monday it would suspend some arms exports to Israel, citing a "clear risk" they could be used in a serious breach of international humanitarian law.
Israeli Defence Minister Yoav Gallant said he was "deeply disheartened" by London's decision, while the premier said he sought forgiveness for failing to save the latest hostages killed.
"Hamas will pay a very heavy price for this," he said during a televised press conference as he rejected making any "concessions" in Gaza ceasefire talks.
Abu Obeida, spokesman for Hamas's armed wing the Ezzedine Al-Qassam Brigades, said remaining hostages would return "inside coffins" if Israel maintains its military pressure on Gaza.
A statement said "new instructions" had been given to militants guarding the captives on what to do if Israeli troops approached.
In Washington, Biden met US negotiators working alongside Qatar and Egypt to try to secure a truce deal that would free the remaining hostages in Gaza in return for Palestinian prisoners held in Israel.
Asked by reporters if he thought Netanyahu was doing enough to secure a deal for the release of hostages, Biden replied: "No."
Netanyahu said Monday Israel must retain control of the key Philadelphi Corridor on the Gaza-Egypt border -- a significant sticking point in negotiations.
"Hamas has to make the concessions," said Netanyahu, whose critics have accused him of prolonging the war to stay in power.
Israelis were gripped by grief and fury after the military said Sunday the bodies of six hostages, all captured alive during Hamas's October 7 attack on southern Israel that triggered the war, were recovered from southern Gaza.
A strike announced by the Histadrut trade union seeking a hostage deal brought parts of Israel to a standstill Monday, although some cities were largely unaffected.
"This is our last chance! Deal now!" protesters chanted as thousands marched Monday through the streets of Tel Aviv.
"Our hearts are burning" and "Enough with this blood government" read signs held by demonstrators as they pushed for a deal to free the remaining 97 hostages, including 33 the military says are dead.
Outside Netanyahu's Jerusalem home, protester Karem Saar said "it's his responsibility to get his citizens out" of Gaza.
"Hamas are the ones that pulled the trigger but the fact that they're still there is on Netanyahu," she told AFP.
Of 251 hostages seized on October 7, just eight have been rescued alive by Israeli forces, although scores were released during a one-week truce in November -- the only one so far.
With Gaza lying in ruins and the majority of the 2.4 million residents forced to flee, often taking refuge in cramped and unsanitary conditions, disease has spread.
After the first confirmed polio case in 25 years, a vaccination drive got underway Sunday with localised "humanitarian pauses" to the fighting.
However, an AFP journalist reported troops blowing up homes in Gaza City and warplanes hitting a house to the east overnight into Tuesday.
The territory's civil defence agency said Israel carried out a deadly strike on a tent sheltering displaced people in southern Khan Yuins, as well as bombarding central Gaza.
Around 160,000 children received a first polio vaccine dose on Sunday and Monday in central Gaza, the territory's health ministry said.
Palestinian mother Basma al-Batsh told AFP on Sunday she was "very happy" the vaccination drive was happening.
"I want to protect my children because I was afraid that they would be affected and become disabled," she said.
Israel's military campaign against Hamas has so far killed at least 40,786 people in Gaza, according to the territory's health ministry. The UN rights office says most of the dead are women and children.
The October 7 attack on Israel resulted in the deaths of 1,205 people, mostly civilians and including hostages killed in captivity, according to an AFP tally based on Israeli official figures.
Since the war erupted violence has surged in Israel's border area with Lebanon and in the occupied West Bank, where the Israeli military launched a large-scale offensive on Wednesday.
Imad Naim Abu Al-Hayat, a Jenin resident, said his barbershop was destroyed by the Israeli military, which has occupied the West Bank since 1967.
"They want to destroy the country so that people get tired of the (Palestinian) resistance, but we will not get tired of the resistance," he told AFP beside a pile of rubble.
Further south in Tulkarem, an Israeli airstrike targeted an "armed terrorist cell" late Monday which the military said had shot at security forces.
Separately, a medical source at Tulkarem's governmental hospital said Israeli forces killed a boy by shooting him in the head.
The Ramallah-based Palestinian health ministry said Monday at least 26 Palestinians have been killed in the northern West Bank since Wednesday.
Three Israeli police officers were also killed in a shooting Sunday in the southern West Bank, an area where three Palestinians have also been killed in recent days according to the territory's health ministry.
In Lebanon, the health ministry said an Israeli strike on a vehicle in the south killed two people Monday.