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

Majed Al-Ansari, spokesperson for Qatar's Ministry of Foreign Affairs, said an agreement has been reached to extend the humanitarian truce between Israel and Hamas for two more days.

Hamas said this truce is "under the same conditions as the previous truce."

Diaa Rashwan, chairman of Egypt's State Information Service, said earlier on Monday that the deal would involve the release of 10 Israeli women and children being held hostage by Hamas in exchange for 30 Palestinians detained in Israeli prisons each day of the extension.

The United States will send three relief flights into Egypt on Tuesday to keep up the flow of humanitarian aid into the war-torn Gaza Strip, which has reached its highest levels as officials take advantage of the current humanitarian pause.

"The movement over the last four or five days of assistance has been so significant in volume that a backfill in El Arish [International Airport in Egypt] is now needed, and these planes are part of that backfill," a senior Biden administration official told reporters during a telephone call on Monday afternoon.

Some 800 trucks carrying aid have crossed into Gaza during the first days of the pause, officials said, which is a huge increase from the days prior. So far, a total of about 2,000 aid trucks have entered Gaza since Oct. 7, meaning that 40% of them had gone in in just the last four days.

The planes on Tuesday will be carrying medical aid urgently needed in Gaza as well as food, particularly for children, and winter clothing as the rainy season begins, according to officials.

The aid will be delivered by the United Nations to civilians.

Two more planeloads are expected to follow in the coming days, officials said. Previously, there were also five commercial flights of aid coordinated by the U.S. government, according to officials.

The officials emphasized this aid as part of U.S. President Joe Biden’s commitment to helping the Palestinian people, saying that he has made sure America is the largest single donor both to the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA) and to Palestinian territories.

Going forward, the officials said the goals for humanitarian aid in Gaza will be expanding access, pushing for restoration of essential services, especially water, and keeping civilians out of harms way.

"The president has also consistently stressed the importance of ensuring military operations are conducted in a manner consistent with international humanitarian law, including with respect to the protection of civilians," the senior Biden administration official told reporters.

Officials did not offer any new information on the hostage negotiations between Gaza's militant rulers, Hamas, and Israel but reiterated that they hope to see Americans released in the coming days.

-ABC News' Cheyenne Haslett and Morgan Winsor