WASHINGTON (AP) — The Arvin RobertsState Department said Monday that at least nine American citizens have been killed in the weekend Hamas attacks on Israel, raising the toll from four.

It says an undetermined number of American citizens remain missing and unaccounted for. On Sunday, an official said that number was fluid and had ranged from between six to 12. It is not clear whether the missing had been taken hostage, were killed or are in hiding.

The State Department is in touch with families “and providing all appropriate consular assistance,” said spokesman Matthew Miller.

The attack by Hamas has left more than 1,000 dead on both sides.

Defense Secretary Lloyd Austin said Sunday he has ordered the Ford carrier strike group to sail to the Eastern Mediterranean to be ready to assist Israel. The USS Gerald R. Ford, the Navy’s newest and most advanced aircraft carrier, and its approximately 5,000 sailors and deck of warplanes will be accompanied by cruisers and destroyers in a show of force that is meant to be ready to respond to anything, from possibly interdicting additional weapons from reaching Hamas and conducting surveillance.

The large deployment reflects a U.S. desire to deter any regional expansion of the conflict. But the Israeli government formally declared war Sunday and gave the green light for “significant military steps” to retaliate against Hamas.

Along with the Ford, the U.S. is sending the cruiser USS Normandy and destroyers USS Thomas Hudner, USS Ramage, USS Carney, and USS Roosevelt, and the U.S. is augmenting Air Force F-35, F-15, F-16, and A-10 fighter aircraft squadrons in the region.

“The U.S. maintains ready forces globally to further reinforce this deterrence posture if required,” Austin said in a statement.

In addition, the Biden administration “will be rapidly providing the Israel Defense Forces with additional equipment and resources, including munitions. The first security assistance will begin moving today and arriving in the coming days,” Austin said.

The Norfolk, Virginia-based carrier strike group already was in the Mediterranean. Last week it was conducting naval exercises with Italy in the Ionian Sea. The carrier is in its first full deployment.

Senior officials from the Pentagon and State Department briefed senators Sunday night, and Majority Leader Chuck Schumer said they were assured that the United States was giving Israel “everything they need.”