New Jersey Sen. Cory Booker arrived in Israel on Friday for several days of planned meetings and was in Jerusalem when the attacks began, Maya Krishna-Rogers, a spokesperson, said in a statement Sunday.

He sheltered in place with his staff and safely departed the country earlier Sunday, according to the statement.

Booker was in Israel for "planned meetings and site visits ahead of the start of an Abraham Accords-focused N7 summit on regional economic integration in Tel Aviv, at which he was scheduled to speak on Tuesday," the statement read.

-ABC News' Mariam Khan

The U.N. agency for Palestinian Refugees said more than 20,000 people are sheltering in schools around Gaza.

-ABC News' Joe Simonetti

The IDF said it's evacuating Israeli civilians from at least two dozen towns along the Gaza border within the next 24 hours.

-ABC News' Joe Simonetti

The U.S. is sending a carrier strike group to the eastern Mediterranean to bolster deterrence in the region and "will be rapidly providing the Israel Defense Forces with additional equipment and resources, including munitions," according to a statement from Defense Secretary Lloyd Austin on Sunday.

"Today, in response to this Hamas attack on Israel, and following detailed discussions with President Biden, I have directed several steps to strengthen Department of Defense posture in the region to bolster regional deterrence efforts," he said.

The U.S. materiel support will begin shipping today and will arrive in the coming days, according to Austin.

The strike group will include the USS Gerald R. Ford aircraft carrier, the guided-missile cruiser USS Normandy and four guided-missile destroyers -- the USS Thomas Hudner, USS Ramage, USS Carney and USS Roosevelt, Austin said.

The U.S. will also boost its F-35, F-15, F-16 and A-10 fighter squadrons in the region, according to the defense secretary.

"The U.S. maintains ready forces globally to further reinforce this deterrence posture if required," he said.

-ABC News' Matt Seyler

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