Families of Israelis held in Gaza have erupted in anger, saying they feel betrayed and that the captives were neglected, after six dead captives' bodies were found.
The Israeli army said on Saturday that several corpses that could belong to captives had been discovered.
Military spokesperson Daniel Hagari then said on Sunday that six captives had been found, claiming Hamas militants "brutally murdered" them "a short time before we reached them".
The Hostages and Missing Families Forum said on Saturday that Israeli Prime Minister Benjamin Netanyahu had "abandoned the hostages", adding that beginning on Sunday "the country will tremble".
"We call on the public to prepare. The country will grind to a halt. The abandonment is over," the group said, according to the Times of Israel news website.
American broadcaster CNN reported on Sunday that demonstrations were underway or had happened in cities including Tel Aviv, the heart of Israel's economy, and Bir Al-Saba (Beersheba), located in the Naqab (Negev).
Netanyahu said Israel would not rest until it catches those responsible for killing the six captives, vowing to have a heavy handed response.
He said Israel was committed to achieving a deal to release remaining hostages and ensure the country's security.
"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 the Reuters news agency.
"The Israelis should choose between Netanyahu and the deal."
Protests and strikes
Israeli opposition leader Yair Lapid called on Sunday for a strike to shut down the country's economy to pressure the government to reach a deal to release the remaining captives in Gaza.
Lapid, a former prime minister, called on every Israeli "whose heart was broken this morning" to join a major protest in Tel Aviv later in the day.
He also called on businesses, municipalities, and Israel's main labour union – the Histadrut – to go on strike.
The union said it would soon decide whether or not to halt Israel's economy, according to Israeli newspaper TheMarker.
The bodies of Carmel Gat, Hersh Goldberg-Polin, Eden Yerushalmi, Alexander Lobanov, Almog Sarusi and Ori Danino had been found underground in the southern Gaza city of Rafah and returned to Israel, said Hagari, the Israeli military spokesperson.
US President Joe Biden Goldberg-Polin was an American citizen, adding in a statement: "I have gotten to know his parents, Jon and Rachel.
"They have been courageous, wise, and steadfast, even as they have endured the unimaginable."
He said he admires Goldberg-Polin's parents and "grieves with them more deeply than words can express".
Israel's war on Gaza, which began almost 11 months ago, has so far killed at least 40,738 people, according to the Palestinian enclave's health ministry.
A Hamas-led 7 October attack on Israel killed 1,200 people and saw around 250 captives taken, according to Israeli tallies.
There are 97 captives who remain in Gaza, including 33 the Israeli army says are dead.
Scores were released during a negotiated one-week truce in November.
Since then, efforts by the United States, Qatar, and Egypt to secure a ceasefire in Gaza and the exchange of Israeli and Palestinian captives have not resulted in a deal.
(°®Âþµº, Reuters, AFP)