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

In remarks with Israeli Prime Minister Benjamin Netanyahu, Secretary of State Antony Blinken said at least 25 Americans had now been confirmed dead in Israel.

Netanyahu described some of the atrocities committed by Hamas.

"Hamas has shown itself to be an enemy of civilization: The massacring of young people in an outdoor music festival, the butchering of entire families, the murder of parents in front of their children and the murder of children in front of their parents. The burning of people alive, the beheadings," he said.

"Hamas should be treated exactly the way ISIS was treated," he said. "They shouldn't be spit out from the community of nations. No leader should meet them. No country should harbor them. And those that do should be sanctioned."

Blinken said he was speaking not only as an American diplomat, but as a Jew, a husband and a father of young children, saying it was impossible for him to look at photos of families killed "and not think of my own children."

"The same time that we've been shocked by the depravity of Hamas, we've also been inspired by the bravery of Israel citizens," he said. "The grandfather who drove over an hour to a kibbutz under siege, armed only with a pistol and rescued his kids and grandkids. The mother who died shielding her teenage son with her body, giving her life to save his -- giving him life for a second time."

Blinken remarked that some U.S. aid had already been delivered, and that more military aid was on his way. He said the administration would work with Congress to meet Israel’s additional needs and that bipartisan support for Israel was "overwhelming."

The secretary called on world leaders to condemn Hamas.

Blinken also reiterated that Israel "has the right -- indeed, the obligation -- to defend itself" but that it was "so important to take every possible precaution to avoid harming civilians."

-ABC News' Shannon Crawford