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."

As the Biden administration intensifies efforts to help American nationals leave Israel and Gaza, more than 20,000 U.S. citizens have reached out to the State Department asking for help in the wake of the Hamas attacks, including several hundred seeking to leave Gaza, according to two U.S. officials.

While not all have actively sought assistance with transportation, "many thousands" across Israel have indicated they needed help finding flights out of the country, the officials said.

Government-chartered planes have now started to ferry U.S. citizens from Israel to other countries in the region, though one official said the State Department still cannot share a detailed breakdown on the number of Americans whose departure it has already facilitated or the number of Americans still waiting for help "given this is an unfolding situation."

For Americans in Gaza, the U.S. is still eyeing the Rafah border crossing between Gaza and Egypt as a means of safe passage. Officials say they are very hopeful they will be able to work with Israel and Egypt to establish a corridor for U.S. citizens and other foreign nationals, but that it could take days to make substantial progress.

The Israeli government estimated that between 100 to 130 Americans were living in Gaza earlier this year. An official says the State Department believes hundreds more are visiting -- putting the total number in Gaza potentially between 500 and 600.

The State Department estimates that roughly 500,000 American citizens reside in Israel.

-ABC News' Shannon K. Crawford