Hamas says talks with Israel about further steps in the Gaza ceasefire deal are conditional on Palestinian prisoners being freed as agreed.

Israel said on Sunday it was delaying the release of more than 600 Palestinians in return for six living and four dead hostages who had been freed, accusing Hamas of repeated violations including “humiliating” handover ceremonies.

A senior Hamas official said the decision exposed the entire agreement to “grave danger” and called on mediators, especially the US, to pressure Israel.

The deal’s first phase and temporary six-week truce is set to expire on Saturday but indirect negotiations on the second phase and an end to the war have not yet begun.

UN Secretary General António Guterres warned that the ceasefire was “precarious” and that a resumption of hostilities must be avoided at all costs.

He also called for the “dignified release of all remaining hostages”.

On Saturday – the start of the sixth and final week of the ceasefire deal’s first phase – Hamas released six living Israeli hostages.

As with many of the previous handovers, five of them were led onto stages beside armed fighters before being transferred to the Red Cross and then taken to Israel.

Later, Hamas posted a video of two other hostages in a vehicle watching one of the handover ceremonies and appearing to plead with Israeli Prime Minister Benjamin Netanyahu to get them out too. A forum representing the hostages’ families condemned the video as a “sickening display of cruelty”.

There was already fury in Israel after Hamas returned the bodies of four hostages earlier in the week, including those of Shiri Bibas and her two young sons Ariel and Kfir, who were abducted during the 7 October 2023 attacks on Israel.

It emerged on Friday that Hamas had handed over the remains of a Palestinian woman rather than those of Ms Bibas. The group said there had been a mistake and transferred Ms Bibas’s body later that day.

Israeli authorities also said a post-mortem had shown that Ariel and Kfir’s captors killed the boys “with their bare hands”, contradicting Hamas’s claim that they died in an Israeli air strike.

Israel was scheduled to free 620 Palestinian prisoners in exchange for the 10 hostages. More than 400 were Gazans detained by Israeli forces during the war, while 50 of the prisoners were serving life sentences in Israeli jails.

They had reportedly already boarded buses at a prison in the occupied West Bank when the order came to suspend their release while Netanyahu consulted ministers.

In the early hours of Sunday, the prime minister’s office said the release would be postponed “in light of Hamas’s repeated violations, including the ceremonies that humiliate our hostages and the cynical exploitation of our hostages for propaganda purposes”.

“It has been decided to delay the release of terrorists that was planned for yesterday until the release of the next hostages has been assured, and without the humiliating ceremonies.”

Hamas – which is proscribed as a terrorist organisation by Israel, the US, UK and other countries – denounced Israel’s decision as a “blatant violation” of the deal and warned US, Qatari and Egyptian mediators that there could be no talks on extending the ceasefire until the prisoners were released.

“We have conveyed a clear and strong message to the mediators – we cannot continue discussing any further steps if these 620 Palestinians are not released,” Hamas political bureau member Basem Naim said in an interview with Al Jazeera on Monday.

Asked if the scheduled release of the bodies of another four Israeli hostages on Thursday could be affected, he replied that “all options are on the table”.

“Before going to the next step, we have to be sure that the past step [will happen],” he added.

“Netanyahu is clearly sending strong messages that he is intentionally sabotaging the deal, he is preparing the atmosphere for returning back to the war. Therefore, what are the guarantees that he might take the other four bodies and again not release the agreed-upon number of Palestinians, plus the 620 Palestinians?”

Naim said Hamas had discussed Israel’s complaints about the hostage handover ceremonies, but denied they had been humiliating and alleged that Israeli authorities had mistreated Palestinian prisoners before they were released.

The White House backed Israel’s decision to delay the prisoner release, saying it was an “appropriate response” to what it called the “barbaric treatment” of hostages by Hamas.

But President Donald Trump’s Middle East envoy, Steve Witkoff, said he would travel to the region this week with the aim of getting “an extension of phase one”.

“We’re hopeful that we have the proper time… to begin phase two, and finish it off and get more hostages released,” he told CNN on Sunday.

A total of 33 Israeli hostages are supposed to be exchanged for about 1,900 Palestinian prisoners and detainees from Gaza during the ceasefire deal’s first phase.

So far, 25 living hostages and four dead hostages have been released, while the bodies of the last four hostages are scheduled to be handed over this week. Five living Thai hostages have also been freed outside the deal.

The agreement has also seen Israeli forces withdraw from densely populated areas of Gaza. Hundreds of thousands of displaced Palestinians have been allowed to return to their homes in the north and hundreds of aid lorries are now being allowed into the territory each day.

The ceasefire’s second phase should see the remaining hostages released, a full Israeli withdrawal and a permanent ceasefire.

The Israeli military launched a campaign to destroy Hamas in response to an unprecedented cross-border attack on 7 October 2023, in which about 1,200 people were killed and 251 were taken hostage.

At least 48,346 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.

Most of Gaza’s population has also been displaced multiple times, almost 70% of buildings are estimated to be damaged or destroyed, the healthcare, water, sanitation and hygiene systems have collapsed, and there are shortages of food, fuel, medicine and shelter.