Massive protests swept Israel on Sunday following the death of six hostages in Gaza as frustration mounted over the failure of the country's leadership to secure a ceasefire deal that would free Israeli captives.

Crowds estimated by Israeli media to number up to 500,000 strong demonstrated in Jerusalem, Tel Aviv and other cities, demanding that Prime Minister Benjamin Netanyahu do more to bring home the remaining 101 hostages, about of a third of whom Israeli officials estimate have died.

In Jerusalem, protesters blocked streets and demonstrated outside the prime minister's residence. Aerial footage showed Tel Aviv's main highway filled with protesters holding flags with pictures of the slain hostages.

Israeli television footage showed police directing water canons at demonstrators who had blocked roads. Local media reported 29 arrests.

The Israeli military announced the recovery of the bodies from a tunnel in the southern Gaza city of Rafah, as a polio vaccination campaign began in the war-shattered Palestinian territory and violence flared in the occupied West Bank.

The bodies of hostages Carmel Gat, Hersh Goldberg-Polin, Eden Yerushalmi, Alexander Lobanov, Almog Sarusi and Ori Danino were returned to Israel, military spokesperson Rear Admiral Daniel Hagari told reporters.

A forensic examination determined they were "murdered by Hamas terrorists in a number of shots at close range" 48-72 hours previously, an Israeli health ministry spokesperson said.

Netanyahu, who faces growing calls to end nearly 11 months of war with a deal for a ceasefire and the release of remaining hostages, said Israel would not rest until it caught those responsible. "Whoever murders hostages - does not want a deal," he said.

Senior Hamas officials said that Israel, in its refusal to sign a ceasefire agreement, was to blame for the deaths.

"Netanyahu is responsible for the killing of Israeli prisoners," senior Hamas official Sami Abu Zuhri told Reuters. "The Israelis should choose between Netanyahu and the deal."

Israel's assault on Gaza began after Hamas and other militants killed about 1,200 people and took about 250 hostages in attacks on Israel on Oct. 7, according to Israeli tallies.

Since then, Israel's offensive has levelled much of the enclave of 2.3 million people, and the Gaza health ministry says at least 40,738 Palestinians have been killed. Displaced people are living in dire conditions with inadequate shelter and a hunger crisis.

'HAMAS WILL PAY,' BIDEN SAYS

Amid mounting public anger, the head of Israel's trades union federation, Arnon Bar-David, on Sunday called for a general strike on Monday to pressure the government into signing a deal, and said Ben Gurion airport, Israel's main air transport hub, would be closed from 8 a.m. (0500 GMT).

Defence Minister Yoav Gallant, who has clashed frequently with Netanyahu, also called for an agreement, and opposition leader and former Prime Minister Yair Lapid urged people to join the demonstration in Tel Aviv.

In a last-ditch bid to stop the demonstrations, Finance Minister Bezalel Smotrich, a hardline member of Israel's security cabinet, asked the attorney general to prohibit the strike.

The Hostage Families Forum called on Netanyahu to take responsibility and explain what was holding up an agreement.

The six hostages brought home on Sunday "were all murdered in the last few days, after surviving almost 11 months of abuse, torture, and starvation in Hamas captivity. The delay in signing the deal has led to their deaths and those of many other hostages," it said.

Netanyahu's office said he had spoken to the family of Lobanov, whose body was among those recovered, apologising and expressing "deep sorrow".

But the family of Gat said they refused to speak to the prime minister and instead called on Israelis to join protests.

"Take to the streets and shut down the country until everyone returns. They can still be saved," Gat's cousin, Gil Dickmann, wrote on X.

U.S. President Joe Biden said he was "devastated and outraged" by the death of 23-year-old Israeli American Goldberg-Polin and the other hostages.

"Hamas leaders will pay for these crimes. And we will keep working around the clock for a deal to secure the release of the remaining hostages," he said in a statement.

Speaking to reporters in Rehoboth Beach, Delaware, he said he was "still optimistic" about a ceasefire deal.

Months of stop-start negotiations mediated by the United States, Qatar and Egypt have so far failed to secure a deal, despite increased U.S. pressure and repeated trips by top officials to the region.

Speaking to Al-Jazeera television, chief Hamas negotiator Khalil Al-Hayya, based in Qatar, on Sunday reaffirmed the group would not sign an agreement unless Israel fully withdrew from Gaza Strip, including the Philadelphi and Netzarim corridors, issues that have been sticking points in the talks.

POLIO VACCINATIONS

Israel and Hamas agreed to pause fighting in areas of Gaza for at least eight hours daily from Sunday to Tuesday to begin vaccinating 640,000 children against polio.

Children, escorted by family members, crowded a UN clinic in the central Gaza city of Deir Al-Balah, according to Palestinian officials. The territory's health ministry said at least 72,611 children were vaccinated the first day.

The campaign comes after the confirmation last month that a baby was partially paralysed by the type 2 polio virus, the first such case in the territory in 25 years.

Israeli forces continued to battle Hamas-led militants in several parts of Gaza, with the Israeli military targeting what it said was a Hamas command centre in a former school in Gaza City. The Palestinian Civil Emergency Service said 11 people had died and medics said many others had been wounded.

In Khan Younis, an Israeli air strike killed two Palestinians and wounded 10 others, according to medics, bringing the day's total death toll in Gaza to 27.