The death toll has risen after Hamas fired rockets into Israel from Gaza in a surprise attack and Israel declared war.

According to Israeli officials, at least 40 people have died in Israel and more than 700 people have been injured. The Palestinian Health Ministry said 160 people were killed in Gaza and over a 1,000 others were injured.

According to Al Jazeera, Israeli forces have surrounded a house in the Israeli settlement of Ofakim and negotiations are underway with Palestinian fighters who are allegedly holding hostages. According to the Jerusalem Post, dozens of hostages are being by Hamas in the Kibbutz Be’eru in southern Israel.

President Joe Biden was briefed Saturday "on the appalling Hamas terrorist attacks in Israel," according to the White House.

"Senior national security officials briefed the President this morning on the appalling Hamas terrorist attacks in Israel. The President will continue to receive updates and White House officials remain in close contact with Israeli partners," the White House said in a statement.

-ABC News' Fritz Farrow

U.S. Defense Secretary Lloyd Austin released a statement saying he is "closely monitoring" the situation in Israel and extended his condolences to the families of those who have lost their lives.

"Over the coming days the Department of Defense will work to ensure that Israel has what it needs to defend itself and protect civilians from indiscriminate violence and terrorism," Austin said.

Separately, a U.S. defense official said that Austin had a call with his team Saturday morning, including U.S. Centcom Commander Gen. Eric Kurilla. Israel falls under Centcom’s area of responsibility.

-ABC News' Luis Martinez

Israeli Prime Minister Benjamin Netanyahu made a video statement on social media, saying simply, “We are at war. We will win," in his first comments, made in Hebrew, after the attack.

"Citizens of Israel, we are at war, not in an operation or in rounds, but at war. This morning, Hamas launched a murderous surprise attack against the State of Israel and its citizens. We have been in this since the early morning hours. I convened the heads of the security establishment and ordered – first of all – to clear out the communities that have been infiltrated by terrorists," Netanyahu said. "This currently is being carried out. At the same time, I have ordered an extensive mobilization of reserves and that we return fire of a magnitude that the enemy has not known. The enemy will pay an unprecedented price. In the meantime, I call on the citizens of Israel to strictly adhere to the directives of the IDF and Home Front Command. We are at war and we will win it."

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