The death toll keeps climbing after Hamas’s coordinated attack on Israel over the weekend. More than a thousand Israelis and Palestinians have been killed, while officials have confirmed some Americans casualties. Israel, which has responded with airstrikes in Gaza, formally declared war on the militant group Sunday. Prime Minister Benjamin Netanyahu vowed that Israel would take “mighty vengeance” as his country embarks on a long and difficult war that was “forced upon us.” The Israeli government says Hamas has taken at least 100 civilians hostage. Meantime, the Pentagon is moving U.S. Navy ships and military aircraft closer to Israel in a show of support.

Secretary of State Antony Blinken says there are reports of “several” Americans in Israel who were killed after Hamas’ surprise attacks. Speaking on CNN’s State of the Union, Blinken said the White House is “working overtime” on verifying information on U.S. citizens in Israel. He added that there are also reports of Americans who are missing, but he didn’t indicate if any of them are being held captive. Blinken re-emphasized U.S. support for Israel and implied there will be more information soon about specific “additional” requests made by Israel.

The White House says it’s too early to determine if Iran was directly involved in Saturday’s Hamas attacks on Israel. Deputy National Security Advisor John Finer says the Biden administration is keeping a close watch on any role Iran or any parties do play moving forward. Finer specifically mentioned Hezbollah, which said on Sunday that it launched rockets and artillery out of Lebanon into Israel. Finer reiterated President Biden’s warning that parties “hostile to Israel” do not exploit Hamas’ attacks for their own purposes.