At least three Americans killed in attacks in Israel near Gaza border, according to memo

At least four Americans have been killed in the attacks in Israel, and US officials expect the death toll to rise, Sen. Chuck Schumer said Sunday.

The Senate majority leader said in a statement that he was briefed Sunday evening by senior national security and State Department officials.

"Unfortunately, we know there are Americans who were killed. The Administration told us that they know of four thus far, but, sadly, we know the toll will rise," Schumer, a Democrat, said in a statement.

Earlier Sunday, Secretary of State Antony Blinken said the US was "working overtime" to verify reports of missing and dead Americans after Hamas launched an unprecedented attack against Israel.

"We have reports that several Americans were killed. We're working overtime to verify that. At the same time, there are reports of missing Americans and there again, we're working to verify those reports," Blinken told CNN's Dana Bash on "State of the Union."

CNN reported earlier Sunday that at least three Americans were killed, according to an internal US government memo. The memo said the State Department was aware of additional Americans who have not been accounted for.

CNN has reached out to the State Department for comment.