Israel was hit by massive protests late Sunday after its military found the bodies of six more Gaza captives.

The mass protests come as frustration mounted over the failure of the country's leadership to secure a cease-fire and hostage exchange deal.

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 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.

Labor leaders called a one-day general strike on Monday.

The Israeli military announced the recovery of the bodies, allegedly 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 Adm. Daniel Hagari told reporters.

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

Netanyahu, who faces growing calls to end nearly 11 months of war with a deal for a cease-fire 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 cease-fire 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 genocidal war on Gaza was triggered by the Oct. 7 Hamas incursion, which caused around 1,200 deaths and took about 250 hostages, according to Israeli tallies.

Since then, Israel's brutal offensive has killed at least 40,738 Palestinians and leveled much of the enclave of 2.3 million people. Displaced people are living in dire conditions with inadequate shelter and a hunger crisis.

Biden threatens Hamas

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. (5 a.m. 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 Sunday died in the last few days, after surviving almost 11 months in captivity, they said, adding that: "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, apologizing 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 cease-fire 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 the Gaza Strip, including the Philadelphi and Netzarim corridors, issues that have been sticking points in the talks.