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

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