The seventh hostage-prisoner exchange under a fragile Gaza ceasefire was set to go ahead on Saturday, despite an outpouring of grief and anger in Israel after Hamas returned the remains of two child hostages without their mother's.

Prime Minister Benjamin Netanyahu slammed Hamas as "monsters" and "savages" on Friday, accusing the Palestinian militant group of murdering young Ariel and Kfir Bibas, whose bodies were returned to Israel the day before.

Hamas had said their mother Shiri Bibas was also among the four bodies handed over Thursday, but Israeli analysis concluded the remains were not in fact hers. 

The group admitted "the possibility of an error or mix-up of bodies", which it attributed to Israeli bombing of the area.

But Netanyahu vowed to "ensure that Hamas pays the full price for this cruel and evil violation of the agreement".

Following Netanyahu's threat, Hamas affirmed its "full commitment" to the ongoing ceasefire deal, which has so far seen 19 living Israeli hostages freed from Gaza in exchange for more than 1,100 Palestinian prisoners released from Israeli jails.

The group's armed wing also confirmed it would release six living Israelis Saturday in the seventh swap since the ceasefire began.

They are the last living hostages eligible for release under the truce deal's first phase, which is due to expire in early March. Hamas has also promised to hand over four more bodies next week.

The Palestinian Prisoners' Club advocacy group said Friday that Israel would free 602 inmates on Saturday as part of the exchange.

A spokeswoman for the NGO told AFP that 445 were Gazans arrested after the war began, while 60 were serving long sentences, 50 were serving life sentences and 47 were re-arrested after being freed in a 2011 prisoner exchange.

She added that 108 of the prisoners would be deported outside of Israel and the Palestinian territories after their release.

Rage and frustration

Since their abduction on 7 October 2023 during the Hamas attack that sparked the war, Shiri, Ariel and Kfir Bibas have become symbols of Israel's hostage ordeal.

A fourth body, that of Oded Lifshitz, a veteran journalist and long-time defender of Palestinian rights, was also returned Thursday.

The International Committee of the Red Cross confirmed Friday it had transferred more human remains to Israel "at the request of both parties," but was not able to say if they were Shiri Bibas's.

Israeli military spokesman Lieutenant Colonel Nadav Shoshani said on social media platform X that its representatives are "in contact with the family".

The revelation that Shiri's body was not handed over with her sons' on Thursday, as promised by Hamas, prompted shock and outrage in Israel.

"It has been one of the saddest days that I can remember in my entire life", said Elisheva Flamm Oren, a 66-year-old social worker, adding she felt "rage" towards Hamas and "frustration" towards the Israeli government for not resolving the hostage crisis.

Military spokesman Rear Admiral Daniel Hagari said after an analysis of the remains that Palestinian militants had killed the Bibas boys "with their bare hands".

Hamas, however, has long maintained an Israeli air strike killed them and their mother early in the war.

Shiri's sister-in-law, Ofri Bibas, said Friday that the family was "not seeking revenge right now," while levelling a measure of the blame at Netanyahu, telling him there would be "no forgiveness" for abandoning the mother and her young sons.

Hamas and its allies took 251 people hostage during the October 7 attack. There are 67 hostages still in Gaza, including more than 30 the Israeli military has said are dead.

The Hamas attack resulted in the deaths of 1,214 people, mostly civilians, according to an AFP tally of Israeli official figures.

Israel's retaliatory campaign has killed at least 48,319 people in Gaza, the majority of them civilians, according to figures from the health ministry in the Hamas-run territory that the United Nations considers reliable.