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."

Itay Chen, a 19-year-old American citizen and Israel Defense Forces soldier, was at his IDF base at the Gaza border before he went missing over the weekend, according to his father, Ruby Chen.

"We got a message from him Saturday morning, 6:30 a.m., saying that there is bombing," Ruby Chen told ABC News. "That was the last time that we had any communication with him. Since then, he has been defined officially by the IDF as missing in action."

"My son, a U.S. citizen, is most likely in Gaza as we speak," he said.

The terrified father is pleading for action.

"There are multiple U.S.-Israeli citizens that are in the same situation as we are," he said. "What we are asking from President Biden, in addition to condemning, is being more vicious in his request from the Hamas to abide to international law when it comes to [prisoners of war]. That means that they need to identify each POW that they have. It means that they need to provide and take care of their health and they need to allow the U.N. … to come and visit those prisoners of war."

"Please help me," he said.

-ABC News' Michelle Stoddart