90 Palestinian prisoners released from Israel

The Israeli cabinet will meet on Friday to discuss and ratify the ceasefire deal reached with Hamas, according to a senior Israeli official.

-ABC News' Jordana Miller

A day after a ceasefire between Hamas and Israel was announced, the agreement is being held up by disagreements between the two sides, according to a senior Israeli official.

"The hold up is due to new demands by Hamas that Israel will never agree to. Among them, issues regarding Palestinian Prisoners," an Israeli official told ABC News.

Hamas has denied that it has made more demands and said it is abiding by the ceasefire deal announced on Wednesday and said the ceasefire urgently needs to be implemented.

"Regarding the claims of Netanyahu's office, I confirm that Hamas is committed to what was agreed upon and to the ceasefire agreement that was announced by the mediators; and no amendments were added. I hope that such statements from Netanyahu's office are not an attempt to evade their commitment to the ceasefire agreement," a senior Hamas official told ABC News.

The two sides are also at odds over who controls the Philadelphi corridor -- a stretch of land separating Gaza and Egypt. This has been a sticking point throughout months of negotiations.

Israel is accusing Hamas of making a "last minute demand to change the deployment of IDF forces in the Philadelphi corridor," Israeli spokesman David Mencer said at a press conference Thursday.

Israel wants to retain control of the corridor, saying it needs to do so to prevent the smuggling of weapons to Hamas.

-ABC News' Jordana Miller

White House National Security Council spokesperson John Kirby told "Good Morning America" on Thursday that Hamas is "desperate" for a ceasefire deal in Gaza after more than a year of intense fighting.

"Hamas is in a much weaker position now than they were in May when this deal got put on the table," Kirby said of the ceasefire agreement, a version of which was tabled by President Joe Biden's administration last summer.

"They're also more isolated with a ceasefire with Israel and Hezbollah -- they can't count on Hezbollah coming to their aid, Iran is weaker," Kirby said of Hamas. "There have been a lot of developments that have put Hamas in a situation where they were more desperate to get to a deal. That's where we are."

Pressure from President-elect Donald Trump and his team "sent a strong signal to everybody in the region," including Hamas, the surviving hostages in Gaza and their families, Kirby acknowledged.

"This new Trump team will have to implement this deal which is why President Biden made sure we were keeping them informed and coordinating with them all the way through this process," Kirby said.

Kirby spoke with GMA shortly after Israeli Prime Minister Benjamin Netanyahu's office accused Hamas of trying to renege on parts of the ceasefire agreement, which is yet to be ratified by the Israeli cabinet.

"We're confident that we're going to be able to start implementing it on Sunday," Kirby said, though added there are some "implementing details that still need to be ironed out" with Israel.

As to the future of Gaza, Kirby said Hamas cannot be allowed to remain in control.

"Post-conflict Gaza, all the governance that needs to happen there, meeting the aspirations of the Palestinian people, all that needs to be ironed out, and it's going to have to be done regionally," Kirby said.

A collective day-after plan will have to ensure that "Hamas cannot return, cannot be in power, cannot threaten Israel and yet all the aspirations for safety and security of the Palestinian people can be met, as well as those of the Israeli people."

Of the U.S. hostages slated for possible release, Kirby said the White House knows "several that are still alive."

"We don't have perfect visibility on every single one, but I think we have a pretty good sense," he added. "We know who is going to be coming out in this first tranche. There will be additional Americans coming out in follow-on tranches.

A senior political official confirmed to ABC News that the Israel Defense Forces will remain in the Philadelphi corridor -- the strip of land separating Gaza from Egypt -- throughout the first phase of the nascent ceasefire deal with Hamas.

Israeli troops will remain in the corridor throughout the first 42 days of the ceasefire process, the official said, their footprint remaining at its current size with forces deployed in "outposts, patrols, observations and control along the entire length of the axis."

The official added that if peace talks fail during the first phase of the ceasefire, Israeli forces will stay in the corridor.

-ABC News' Jordana Miller