LONDON — Israeli Prime Minister Benjamin Netanyahu has vowed “revenge” after it alleges one of the four bodies handed over from Gaza to Israel Thursday did not include a hostage.

The Israel Defense Forces called it a “very serious violation” by Hamas After Israeli officials conducted forensic analysis to confirm the identities of the returned bodies only to allege the remains of Lifshitz and Shiri Bibas’ two children were identified, but the fourth body was not Shiri Bibas — nor was it a match for another hostage, the IDF said.

“The cruelty of the Hamas monsters knows no bounds,” Netanyahu said in the statement released Friday. “Not only did they kidnap the father, Yarden Bibas, the young mother, Shiri, and their two small babies. In an unspeakably cynical manner, they did not return Shiri to her little children, the little angels, and they put the body of a Gazan woman in a coffin.”

“We will act with determination to bring Shiri home along with all our hostages – both living and dead – and ensure that Hamas pays the full price for this cruel and evil violation of the agreement,” Netanyahu continued.

Hamas has not responded to the IDF’s findings.

Red Cross officials took custody of four black coffins during a ceremony in the southern Gaza city of Khan Younis on Thursday. A Red Cross official and a Hamas commander appeared on a stage to sign documents as part of the handover. The coffins were also brought onto the stage.

A banner on the stage declared in both Arabic and English: “The Return of War = The Return of Your Prisoners in Coffins.”

An Israeli security official confirmed to ABC News that an IDF-held ceremony took place in the IDF-controlled Gaza buffer zone before the coffins were brought across the border into Israel. The bodies were taken to Israel’s National Center of Forensic Medicine in Tel Aviv’s Abu Kabir neighborhood.

Kfir Bibas was 8 1/2 months old when he was kidnapped by Hamas on Oct. 7, 2023 — the youngest of the 251 hostages taken on the day the group carried out its terror attack on Israel — the worst in the country’s history. In the ensuing war, more than 48,000 Palestinians have been killed in Gaza.

Ariel Bibas was 4 at the time of his death, the IDF said. Both children were determined to have been killed in captivity in November 2023, the IDF said Thursday.

Their father, Yarden Bibas, was also kidnapped and freed earlier this month, the IDF said.

Six other hostages are expected to be released on Saturday and four more bodies will be returned to Israel next week. The hostages who will be released on Saturday have been identified as Eliya Cohen, 27; Tal Shoham, 40; Omer Shem Tov, 22; Omer Wenkrat, 23; Hisham Al-Sayed, 36; and Avera Mengistu, 39, according to Israeli officials and the Hostages and Missing Families Forum.

ABC News’ Nadine El-Bawab, Ellie Kaufman, David Brennan and Morgan Winsor contributed to this report.