Israel-Gaza updates: Israel says ground operation underway in southern Gaza

While the cease-fire extension is expected to bring the release of additional hostages, National Security Council spokesperson John Kirby acknowledged there's a "real risk" that Hamas could benefit the longer the cease-fire continues.

"Without getting into intelligence issues," Kirby said, "any pause in the fighting could benefit your enemy in terms of time to refit, to rest your fighters, to rearm them, reequip them."

Kirby said the cease-fire is a "calculated risk" that Israeli Prime Minister Benjamin Netanyahu is willing to take to get hostages out, and that military operations will resume against Hamas leadership.

-ABC News' Molly Nagle

The U.S. believes there are eight or nine Americans still being held in Gaza, National Security Council spokesperson John Kirby said, adding that the U.S. does not have "solid information on each and every one of them."

Asked if Americans were expected to be released in the coming days, Kirby said the administration "certainly hope[s] so," but did not say more.

"I mean, we're going to watch this very, very closely. We're certainly hoping that another batch of hostages gets released today as part of the fourth and final day of the original agreement. We’re going to be watching closely to see if any Americans are in that group," Kirby said.

"We don't really know until you get into the end game who's going to be actually on that list and then, even then, you got to watch closely [to see] if who's on the list is folks that actually come out," he said.

Kirby was asked specifically about the two American women who were expected to be part of the first round of releases, and he reiterated his hope they would be released Monday.

-ABC News' Molly Nagle

Hamas officials said they've received a list of Palestinian prisoners who are expected to be released from Israel on Monday in exchange for hostages. The list includes three women and 30 children, Hamas officials said.

Muhammad Ibrahim Asfour was among the Gaza residents who returned home during the cease-fire to find destruction where homes used to be.

"I was shocked, and when I saw the house I started crying," Asfour told ABC News. "There were 50 people in the building here -- all of my brothers and father were living here."

"The situation here is more difficult than you can imagine," Abdelkader Darma told ABC News. "When I came home I was shocked."

"People do not know where to go," Darma said. "I and six other people slept on two mattresses and two pillows, which means you do not know how to sleep. They sleep three against three, and you find his feet in front of your face."

“I hope the truce will be extended and a solution will be found because it is enough. People are sleeping in the street," Darma said. "How can you bear it?"

-ABC News' Zoe Magee and Sami Zayara