Israeli Prime Minister Benjamin Netanyahu's office said Thursday that Hamas was attempting to renege "on parts of the agreement reached with the mediators and Israel in an effort to extort last minute concessions."

"The Israeli cabinet will not convene until the mediators notify Israel that Hamas has accepted all elements of the agreement," the statement said.

The Israeli cabinet is due to meet on Thursday to approve the ceasefire agreement that was announced on Wednesday. The ceasefire is due to begin on Sunday.

Officials involved in the matter told ABC News the Israeli negotiating team is still in Doha, Qatar, where negotiations have been held.

-ABC News Bruno Nota and Jordana Miller

The International Committee of the Red Cross said in a statement it is "ready to help implement the agreement reached by the parties and bring hostages and detainees home," as mediators and combatants in Gaza prepare for Wednesday's ceasefire deal to come into effect on Sunday.

The ICRC has previously helped facilitate the release of 109 hostages and 154 detainees, the organization said in its statement, describing such operations as "highly complex" and requiring "meticulous logistical and security planning to minimize the risk to life."

ICRC President Mirjana Spoljaric said she hopes Wednesday's agreement "marks a new beginning."

"Civilian lives must be protected and their needs prioritized," she added.

"The coming days are critical and we are counting on the parties to hold to their commitments. While the agreement is welcome, it is not the end. There are immense humanitarian needs that must be addressed, which will take months, if not years."

Iranian Supreme Leader Ayatollah Ali Khamenei said the Gaza ceasefire deal announced Wednesday showed Israel was "forced to retreat."

"It will be written in books that there was a mob who once killed thousands of children & women in Gaza," Khamenei said in a post to X.

"Everyone will realize" that the patience of Palestinians and the "steadfastness" of Hamas and other militant groups delivered victory over Israel, the Iranian leader said.

Two living Americans are expected to be among the 33 hostages in Gaza released as part of the first phase of the ceasefire deal, a senior administration official told reporters Wednesday.

Keith Siegel and Sagui Dekel-Chen are both expected to be released, with Siegel qualifying for release due to his age and Dekel-Chen because of an injury after being shot on Oct. 7, the official said.

"We're now very hopeful that we begin to see hostages come home as early as Sunday," the official said.

Edan Alexander, a third living American hostage, will fall in the second release phase because of his Israeli military service, the official said, adding that the U.S. remains fully committed to getting him out.

The remains of four American hostages also remain in Gaza, President Joe Biden said. The remains of deceased hostages will be returned in phase three, he said.

-ABC News' Molly Nagle and Kelsey Walsh