More remains of Israeli hostages were handed over by Hamas on Tuesday, as part of a U.S.-brokered deal aimed at keeping peace in Gaza, Israeli authorities said.

Four coffins were transferred to the Red Cross and were on their way to the Israel Defense Forces and Israel Security Agency in the Gaza Strip, according to a joint statement from the IDF and ISA, citing information provided by the Red Cross.

However, the IDF said on Wednesday that one of the bodies handed over by Hamas was not one of the hostages.

“Following the completion of examinations at the National Institute of Forensic Medicine, the fourth body handed over to Israel by Hamas does not match any of the hostages,” the IDF said in a statement. “Hamas is required to make all necessary efforts to return the deceased hostages.”

The remains of the other three hostages were identified as Staff Sergeant Tamir Nimrodi, Uriel Baruch and Eitan Levi, the IDF said. 

“The IDF expresses deep condolences to the families, continues to make every effort to return all the deceased hostages, and is prepared for the continued implementation of the agreement,” the IDF said in a statement Wednesday.

The return of the hostages is a cornerstone of the Gaza peace plan, which called for Hamas to hand over all remaining hostages – 20 living and 28 dead – by Monday, Oct. 13. 

While Hamas returned the 20 living hostages by the Monday deadline, the remains of only four deceased Israeli captives were handed over on Monday. They were identified Tuesday by Netanyahu’s office as Guy Iluz, Israeli military Capt. Daniel Peretz, Yossi Sharabi and Bipin Joshi. 

Israeli Defense Minister Israel Katz said in a social media post on Monday that Hamas’ initial return of only four bodies constituted “a violation of the agreement” and added that “any delay or deliberate avoidance will be considered a gross violation of the agreement and will be responded to accordingly.”

During negotiations that led to the deal, Hamas representatives said they did not know the location of all the remains of deceased hostages, according to Israeli media reports. President Trump also said in Egypt on Monday that not all of the bodies of the deceased hostages had been found, adding that unidentified parties were still “working out” how to locate an unspecified number of remains.

Gal Hirsch, the Hostage and Missing Persons Coordinator for the Israeli Prime Minister’s Office, told CBS News last week that an international team would be established to locate missing hostages in Gaza, but details as to who will form that team and when it might begin its work remained unconfirmed on Tuesday.

The Hostages and Missing Families Forum, which represents Israeli hostage families, has voiced anger that all of the bodies have not been returned and called on the U.S. to leave “no stone unturned in demanding that Hamas fulfil their end of the agreement and bring all of the remaining hostages home.”

In exchange for Israeli hostages, the peace deal stipulated that Israel release nearly 2,000 Palestinian detainees and prisoners held by Israel. It also called for a surge of humanitarian aid to Gaza, and a partial pullback by Israeli forces from the Palestinian territory’s main cities – which happened on Friday and kicked off a three-day window for the return of Israeli hostages.