The senior administration official said that if Israel and Hamas fail to accept this final proposal, it could mark the end of the American-led ceasefire negotiations.

“You can’t keep negotiating this. This process has to be called at some point,” the official told the Post, noting that the US, Egypt, and Qatar had been working on the final proposal before the six captives were found dead in a tunnel in the southern Gaza city of Rafah.

“U.S. officials are going to be burning up the phones over the next 48 hours to see if a deal can still be reached,” another senior US official told the Post.

It was not immediately clear whether the discovery of the six captives' bodies would make it more or less likely that Israel and Hamas could reach an agreement in the coming weeks, the Post's report cited Biden’s administration officials as saying.

A rare call for a general strike in Israel to protest the failure to return captives held in Gaza led to closures and other disruptions around the country on Monday, including at its main international airport.

Tens of thousands of Israelis poured into the streets late Sunday in grief and anger after six captives were found dead in Gaza. The families and much of the public blamed Prime Minister Benjamin Netanyahu, saying they could have been returned alive in a deal with Hamas to end the war in Gaza.

“Netanyahu has never prioritized freeing the hostages. For now, he will be under a lot more domestic pressure to accept a cease-fire deal that saves the remaining hostages,” Frank Lowenstein, a former State Department official who helped lead Israeli-Palestinian negotiations in 2014, told The Washington Post.

He said if Netanyahu waits this out, "over time fewer living captives could mean fewer Palestinian prisoners to release and what he sees as a more favourable negotiating position."

Hamas has blamed the death of the captives on Israel and the United States, accusing them of dragging out the talks by issuing new demands, including lasting Israeli control over the two strategic corridors in Gaza, Philadelphi, along the Gaza-Egypt border and Netzarim which divides northern and southern Gaza.

The group has already offered to release the captives in return for an end to the war, the complete withdrawal of Israeli forces, and the release of a large number of Palestinian prisoners.

A senior Hamas official told AFP on Sunday that several of the six Israeli captives found dead in Gaza "were part of the list of captives to be released that Hamas had approved" in a proposed exchange for Palestinian prisoners held in Israel.

Izzat al-Rishq, a senior Hamas official, said the captives would still be alive if Israel had accepted a US-backed ceasefire proposal that Hamas agreed to in July.

A previous US proposal
 

In early July, Hamas gave initial approval for the outline ceasefire plan announced by Biden on 31 May.

The proposed deal first included a “complete” six-week ceasefire that would see the release of several captives, including women, the elderly, and the wounded, in exchange for the release of hundreds of Palestinian prisoners.

During these 42 days, Israeli forces would also withdraw from densely populated areas of Gaza and allow the return of displaced people to their homes in northern Gaza.

Over that period, Hamas, Israel, and the mediators would also negotiate the terms of the second phase that would see the release of the remaining male captives, both civilians and soldiers. In return, Israel would free additional Palestinian prisoners and detainees.

Additionally, the third phase would see the return of any remaining captives, including bodies of dead ones, and the start of a years-long reconstruction project.

However, a few days after Hamas' approval, Netanyahu added new demands to the deal, including lasting Israeli control over the Philadelphi and the Netzarim corridors.