Israeli National Security Adviser Tzachi Hanegbi said late Wednesday that cease-fire talks with Hamas were still ongoing and no hostages would be released before Friday.
Hanegbi gave no explanation for the delay and it was not immediately clear when the cease-fire might begin.
"Negotiations for the release of our captives are progressing and continue all the time," Hanegbi said in a statement released by the prime minister's office.
Israel's public broadcaster, Kan, citing an Israeli official, reported there was a 24-hour delay in the agreement because the deal was not signed by Hamas and Qatar, which helped broker the deal.
Israel's war cabinet approved on Wednesday a four-day cease-fire with Hamas militants in which militants were to release some 50 hostages held in Gaza.
In exchange, Hamas said Israel will release 150 Palestinian women and children held in Israeli jails.
The deal would also provide aid into the besieged Gaza Strip as thousands remain displaced and in miserable conditions since the conflict broke out on October 7.
The cease-fire agreement had been confirmed by both parties earlier in the day, along with Washington and Qatar.
The European Commission President Ursula von der Leyen "wholeheartedly" welcomed the agreement, as did German Foreign Minister Annalena Baerbock who called the news a "breakthrough."
Egyptian state media had earlier reported the truce would begin Thursday morning.
Yemen's Houthis say they launched missiles at Israel
Yemen’s Houthi rebels said that they launched a batch of long-range large missiles toward southern Israel, including the Red Sea city of Eilat.
The Iran-backed rebel group haslaunched at least six aerial attacks against Israel since the conflict broke out on October 7.
The Houthi are staunch foes of Israel and have vowed to continue aerial attacks and hijackings of Israeli ships.