Women and children account for most of the thousands injured in Gaza from the airstrikes, according to Doctors Without Borders.

Doctors Without Borders said all of the patients they received at one of their clinics in Gaza City were children between the ages of 10 to 14.

Stephanie Hallett, the chargé d'affaires of the U.S. Embassy in Jerusalem, posted a video on X showing her standing in front of the wreckage at Israel's Be'eri kibbutz, where many residents were killed by Hamas terrorists.

"It's really unbelievable," she said, choking up. "As a mother, and just as a human being, to see and to know what happened here, it's really important to say that we've been here, we've seen it, and it is evil. And we stand with Israel."

National Security Council spokesman John Kirby said the U.S. is working with its Israeli and Egyptian counterparts to secure safe passage out of Gaza for civilians.

"Civilians are not to blame for what Hamas has done," Kirby said. "I don't have an announcement to make today -- I can't tell you a specific route or corridor. I just want to make it clear that we are actively working on this with our Egyptian and our Israeli counterparts. Civilians are protected under the laws of armed conflict, and they should be given every opportunity to avoid the fighting."

-ABC News' Molly Nagle

Seventeen Americans are missing, including an unknown number of Americans being held hostage by Hamas, National Security Council spokesman John Kirby said.

"I think we all need to steel ourselves for the very distinct possibility that these numbers will keep increasing and that we may, in fact, find out that more Americans are part of the hostage pool," Kirby said.

He said the conditions and whereabouts of the hostages are not known.

"We don't know where they are, we don’t know if they're all in one group, or broken up into several groups. We don't know if they're being moved, and with what frequency and to what locations. All of those questions we're working hard to answer," he said.

Pressed by ABC News if U.S. officials have seen any proof of life, Kirby said, "I am not aware of any specific proof of live on any individual hostage."

Asked if the U.S. has had any communication with Hamas, directly or through allies, Kirby said, "We're in discussions not only with the Israelis about what hostage recovery can look like, but with other allies and partners in the region. And there are some countries like Qatar that have open lines of communication with Hamas. So, of course, we're casting the net wide."

"We haven't made any policy options or operational decisions with respect to hostage recovery at this time," he said.

Kirby said there is no "specific evidence that Iran was directly involved with these specific sets of attacks" on Israel, but he added, "We are going to keep looking at it -- the book is not closed."

In recent days, the White House has consistently said there was no evidence pointing to Iran’s participation but said Iran was broadly complicit with their past funding and support for Hamas.

-ABC News' Mary Bruce

Human Rights Watch has accused Israel of using white phosphorus munitions in military operations in Gaza on Wednesday, saying it violated international humanitarian law by putting civilians at unnecessary risk.

In a report released Thursday, Human Rights Watch said it based its determination on a video it said it has verified, as well as two eyewitness accounts.

The Israel Defense Forces said in a statement to ABC News that claims they used white phosphorus in Gaza are "unequivocally false."

ABC News geolocated a video showing a jellyfish-shaped plume of white smoke over the port of Gaza. The video was posted on Wednesday by the official Palestinian news agency WAFA and matches images posted on social media and by other news outlets on the day.

Two experts -- Amael Kotlarski, the weapons team manager for the defense intelligence firm Janes, and Amnesty International weapons investigator Brian Castner -- told ABC News that images suggested munitions deployed over the port of Gaza on Wednesday appeared to contain white phosphorus.

"We have verified that Israeli artillery forces striking Gaza are equipped with M825 and M825A1155mm white phosphorus projectiles," Castner told ABC News, pointing to photographs by an Anadolu Agency photographer taken on Monday and showing Israeli troops handling shells labeled "M825A1."

Kotlarski said visual evidence alone was not sufficient to confirm that these specific shells were used in the Gaza port strikes.

There are "perfectly legal" military uses for white phosphorus munitions, Kotlarski said, including to create a smoke screen to conceal movements, to mark targets for artillery or air strikes, or to illuminate a battlefield. However, its use in urban areas is "problematic due to the higher risk of collateral damage," Kotlarski said, including the munitions' potential to cause severe burns.

White House Principal Deputy Press Secretary Olivia Dalton said Friday the U.S. had not independently verified allegations Israel used white phosphorous "so that is not something I would want to speculate about or weigh in on at this time."

-ABC News' Christopher Looft, Ben Gittleson and Jordana Miller