WASHINGTON Three Americans held by Hamas in Gaza since its attack on Israel last month are expected to be among at least 50 hostages to be released by the Islamist Palestinian group under a deal arranged with Israel, the U.S. and Qatar, a senior U.S. official said.

The three include a 3-year-old girl whose parents were among the more than 1,200 people killed in Hamas' initial Oct. 7 attack on southern Israel, the official said. Israeli bombardments since have flattened large swaths of Hamas-led Gaza and killed 13,300 civilians, according to authorities in Gaza.

The official, speaking to reporters on condition of anonymity, said it was likely that more than 50 hostages, largely women and children, will be released once a pause in fighting takes hold.

Under terms of the deal, Hamas is to release 50 hostages and Israel will release 150 Palestinian prisoners during a four- to five-day pause in the fighting.

The hostage group will include two American women and an American girl named Abigail who will turn four on Friday, the official said.

Initial releases of hostages are expected within 24 hours of the deal's announcement, with the first likely to be freed Thursday morning, the official said.

"I would say it's at least 50 of the women and children over a period of four to five days," the official said, without providing details of any other nationalities expected to be released.

The deal will also include more deliveries of humanitarian relief aid to Gaza, the official said. Officials hope the pause will be observed in northern Israel where there have been clashes between Hezbollah and Israeli forces.

A rigorous inspection regime will ensure Hamas does not use the pause to rearm the group's fighters in Gaza with weaponry, the official said.

Hamas has said "they actually need a pause to locate and determine where people are," the official said. The pause will give Hamas time to identify and collect additional women and children, the official said.

"We do anticipate it will be more than 50, but I just don't want to put a number on it," the official said. "But the way the deal is structured is it very much incentivizes the release of everybody."

(Reporting By Steve Holland, Costas Pitas, Humeyra Pamuk and Arshad Mohammed; Editing by Scott Malone and Lincoln Feast.)