The start of a short-term cease-fire between Israel and Hamas that will allow for the release of some hostages held in Gaza, the release of Palestinians being held by Israel and for more humanitarian aid to enter the Gaza Strip has been delayed until Friday, an Israeli official said.

"The contacts on the release of our hostages are advancing and continuing constantly. The start of the release will take place according to the original agreement between the sides, and not before Friday," Israeli National Security Council Director Tzachi Hanegbi said Wednesday in a statement.

The release of hostages, along with a four-day cease-fire, was originally set to begin Thursday morning. A spokesperson for the U.S. National Security Council stressed that the delay did not indicate the deal was in peril.

"The deal was agreed and remains agreed. The parties are working out final logistical details, particularly for the first day of implementation," Adrienne Watson, the NSC spokesperson, said in a statement. "It is our view that nothing should be left to chance as the hostages begin coming home. Our primary objective is to ensure that they are brought home safely. That is on track and we are hopeful that implementation will begin on Friday morning."  

According to the terms of the deal, Hamas will release 50 hostages, all women and children, over the course of four days. Three Palestinian prisoners held by Israel will be released for every Israeli hostage released by Hamas. President Biden said three Americans are among those expected to be released by Hamas. One of the American hostages is a three-year-old girl, the only American child being held by Hamas, but it was not immediately clear if she would be part of the initial release.

There is a possibility more could be released by both sides.

Israeli Prime Minister Benjamin Netanyahu said Tuesday that "the release of every additional ten hostages will result in one additional day in the pause."  

If the first phase of the hostage release goes as planned, roughly 20 more hostages will be released by Hamas and the pause in fighting would be extended.  

Israel has said Hamas militants seized about 240 hostages during their Oct. 7 attack on southern Israel, in which 1,200 people were killed. Four hostages had been released before Wednesday's deal was announced, and another, an Israeli soldier, was rescued by her Israel Defense Forces troops in Gaza. Israel also said two hostages were found dead near the Al-Shifa Hospital in Gaza last week.  

An operation center is expected to be set up in Doha, Qatar, to monitor the hostage transfers. The Qatari government, along with Egypt, was instrumental in helping plan and negotiate the deal.

The neutral International Committee of the Red Cross is expected to take custody of the hostages from Hamas in Gaza and hand them over to the Israel Defense Forces.  

A source familiar with the talks told CBS News that most of the Palestinian prisoners who are released will live in the Israeli-occupied West Bank, though some did come from Gaza.  

During the pause in fighting, aid will be allowed into the Gaza Strip, with 300 trucks per day carrying supplies, including cooking oil for bakeries and fuel for hospitals, a source familiar with the talks told CBS News. 

Prior to a Wednesday meeting of Israel's war cabinet to discuss the hostage deal, Netanyahu stressed in a statement that the pause would not mean an end to the war. 

"There is a lot of nonsense out there to the effect that after the pause to return our hostages, we will stop the war. Then let me make it clear: We are at war — and will continue the war," he said. "We will continue the war until we achieve all of our war aims: To eliminate Hamas, return all of our hostages and our missing, and ensure that there is no element in Gaza that threatens Israel." 

— Margaret Brennan, Kathryn Watson and Tucker Reals contributed reporting.

In:
• Hamas
• Israel
• Ceasefire

Jordan Freiman is an editor and writer for CBSNews.com. He covers breaking news, trending stories, sports and crime. Jordan has previously worked at Spin and Death and Taxes.