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."

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Netanyahu tells Israel in televised address "we are at war"

ABC's audio reporter Jordana Miller gives us details about the surprise attack in Israel.