In a new clip from a "60 Minutes" interview, set to air in full Sunday on CBS, President Biden says he feels strongly about doing this so the families know that their president "cares deeply" about what has happened and will do "everything in our power to get them home if we can find them."

"I think they have to know that the president of the United States of America cares deeply about what's happened to them, deeply. We have to communicate to the world--this is critical, this is not even human behavior. It's pure barbarism. And we're going to do everything in our power to get them home if we can find them," Biden said in the short clip.

-ABC News' Mary Bruce and Molly Nagle

Secretary of Defense Lloyd Austin arrived in Tel Aviv early Friday morning and will meet with Israeli leaders face-to-face to "underscore the unwavering support of the U.S. for the people of Israel and commitment to ensuring Israel has what it needs to defend itself," according to a Department of Defense statement.

"While in Israel, Secretary Austin will meet with Prime Minister Benjamin Netanyahu, Minister of Defense Yoav Gallant, and the Israeli War Cabinet. He will also see firsthand some of the U.S. security assistance delivered to Israel. This is Secretary Austin’s second visit to the country this year, and his third as Secretary of Defense," the statement read.

The U.N. Agency for Palestine Refugees relocated its central operation center and international staff to southern Gaza, the UNRWA said in a post on X early Friday morning local time.

“UNRWA relocated its central operations centre + international staff to the south to continue its humanitarian operations and support to its staff and Palestine Refugees in #Gaza. We urge the Israeli Authorities to protect all civilians in @UNRWA shelters including schools,” the statement read.

The announcement comes as Israel Defense Forces called for "all residents of Gaza City to evacuate their homes" and "move south for their protection" early Friday morning.

-ABC News' Ellie Kaufman

Israel Defense Forces called for "all residents of Gaza City to evacuate their homes" and "move south for their protection" early Friday morning local time in a series of posts on X.

The IDF told residents to move "and settle in the area south of the Gaza River."

The announcement was made, according to the IDF, because it plans to "operate significantly in Gaza City in the coming days" and wanted "to avoid harming civilians."

The IDF said in its posts that it believes Hamas terrorists are hiding in Gaza City, including in buildings with "innocent civilians” inside.

"[D]istance yourself from the Hamas terrorists who use you as a human shield," the post read.

The message was released a short time after the UN made a similar announcement, also citing Israel's military.

-ABC News' Ellie Kaufman

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