National Security Council spokesperson John Kirby avoided saying if the U.S. believed Israel's calls for civilians in Gaza to evacuate in the next 24 hours was possible but acknowledge that it was a "tall order" given how densely populated the area is.

"Well, I think we're going to be careful not to get into armchair quarterbacking the tactics on the ground by the IDF. What I can tell you is we understand what they're trying to do. They're trying to move civilians out of harm's way and giving them fair warning. Now, it's a tall order. It's a million people, and it's a very urban, dense environment, already a combat zone. I don't think anybody's underestimating the challenge here of affecting that evacuation," Kirby said in an interview on CNN Friday morning.

"But it's pretty clear that what they're trying to do is to the maximum extent possible avoid civilian casualties and also separate Hamas from the human shields. I mean, Hamas actually gave a counterorder telling Palestinians in Gaza to stay at home. Why? Because having human shields, they think, protects them," Kirby continued.

Asked about their efforts to secure a safe passage for civilians out of Gaza, Kirby reiterated that the U.S. is talking to Israel and Egypt but would not comment further on progress.

On the Rafah crossing specifically, Kirby said "So far it's still closed. But that doesn't mean were not going to still try as hard as we can to talk to the Israelis and Egyptians about getting it open and having some sort of safe passage out. It's important that we also continue to work to make sure that humanitarian assistance can get in. The United States has no intention of stopping our efforts to continue to deliver humanitarian assistance, but there has to be a path in, there has to be a path out."

Kirby had no update on the Americans who are believed to be held hostage in Gaza and could not confirm reports that 13 hostages have been killed by Israeli airstrikes, as Hamas has claimed.

-ABC News' Molly Nagle

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

The number of hostages being held by Hamas in Gaza is now believed to be 155, Israel Defense Forces said Sunday.

The number of hostages rose from 126 earlier Sunday, the IDF said. An undetermined number of Americans are believed to be among the hostages, according to U.S. officials.