National Security Advisor Jake Sullivan said Tuesday that there are at least 20 Americans missing in Israel amid the ongoing war between Israel and Hamas, which has already claimed the lives of 1,600 people.

Speaking during a press briefing at the White House, Sullivan stressed that while at least 20 Americans are missing in Israel, it doesn't mean they're being held hostage.

"We believe that there are 20 or more American who at this point are missing. But I want to underscore and stress, that does not mean necessarily that there are 20 or more American hostages. Just that is the number who are currently unaccounted for," Sullivan said.

He said that the number of Americans being held hostage by Hamas is currently unknown.

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Israeli soldier seen walking down a street

Israeli soldiers take position at the southern Israeli town of Ofakim on Sunday, after Hamas militants stormed over the border fence Saturday, killing hundreds of Israelis in surrounding communities. The burning car was used by the gunmen and set on fire by the residents.  (AP Photo/Ilan Assayag)

"We will work hour by hour both to determine whether we can account for any of those Americans or to confirm exactly what the number of Americans who are being held hostage," Sullivan said.

Sullivan stressed that the figure of Americans who are unaccounted for could rise.

National Security Adviser Jake Sullivan addresses the press ahead of President Biden's meeting with South Korean and Japanese leaders at Camp David

U.S. National Security Adviser Jake Sullivan (Jim Watson/AFP via Getty Images)

President Biden said during a Tuesday speech that at least 14 Americans have been killed since the war began Saturday morning.

"There are moments in this life, I mean this literally, when the pure, unadulterated evil is unleashed on this world," Biden said. 

"The people of Israel live through one such moment this weekend," he added. "The bloody hands of the terrorist organization Hamas, a group who stated purpose for being is to kill Jews, which was an act of sheer evil."

Biden also said Americans are being held hostage by Hamas.

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President Biden speaks at White House

President Joe Biden speaks Tuesday in the State Dining Room of the White House with Vice President Kamala Harris, left, and Secretary of State Antony Blinken, in Washington, D.C. (Ting Shen/Bloomberg via Getty Images)

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A total of 1,600 people have been killed, with over 1,000 of them being in Israel.

Fox News Digital's Andrea Vacchiano contributed to this report.