President Joe Biden said he spoke with Jordanian King Abdullah II, members of the U.S. Congress and directed his national security team to remain in contact with their Israeli counterparts.

"I've also directed my team to remain in constant contact with leaders throughout the region including Egypt, Turkey, Qatar, Saudi Arabia, Jordan, Oman, UAE, as well as our European partners and the Palestinian Authority," Biden said.

President Joe Biden delivered remarks from the White House on Saturday expressing U.S. support for Israel in light of Hamas' attack.

"We will not ever fail to have their back," Biden said.

"Israel has the right to defend itself and his people full stop. There is never a justification for terrorist attacks and my administration's support for Israel security is rock solid and unwavering. Let me say this as clearly as I can. This is not a moment for any party hostile to Israel to exploit these attacks to seek advantage. The world is watching," Biden said.

Secretary of State Antony Blinken "reaffirmed" the U.S.' solidarity with Israel during a call with Israeli President Isaac Herzog and Foreign Minister Eli Cohen, a State Department spokesperson said.

"Secretary Blinken reiterated his condolences for the victims of the terrorist attacks against Israel and condemned those attacks in the strongest terms," the spokesperson, Matthew Miller, said in a statement. "Secretary Blinken also discussed measures to bolster Israel’s security. The Secretary underscored the United States' unwavering support for Israel's right to defend itself."

President Joe Biden is set to deliver remarks at 2:30 p.m. on the attacks in Israel from the State Dining Room, according to the White House.

-ABC News' Fritz Farrow

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