Secretary of State Antony Blinken said Sunday the US is “working overtime” to verify reports of missing and dead Americans overseas 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.”

The large-scale surprise attack by Gaza militants on Israel on Saturday has left hundreds of Israelis dead, prompting vows of retribution from Israeli Prime Minister Benjamin Netanyahu and a lethal volley of retaliatory Israeli airstrikes.