The US is sending a carrier strike group, a fighter squadron and additional warships to the Middle East as the region braces for an Iranian retaliation to the killing of a senior Hamas leader in Tehran earlier this week.

It is perhaps the largest movement of US forces to the region since the early days of the Gaza war, when the Pentagon sent two carrier strike groups toward the Middle East in a very public warning to regional militant groups not to expand the fighting.

“We’ve heard the Supreme Leader loud and clear that he intends to avenge this killing of a Hamas leader in Tehran, and that they want to conduct another attack on Israel,” John Kirby, the strategic communications coordinator for the National Security Council, told CNN. “We can’t just assume that we are also potentially going to be victims of that kind of an attack, so we’ve got to make sure we’ve got the right resources and capabilities in the region.”

On Friday, Defense Secretary Lloyd Austin ordered the USS Abraham Lincoln strike group to replace the USS Theodore Roosevelt strike group, which is currently operating in the Gulf of Oman, according to a statement from Pentagon deputy press secretary Sabrina Singh.

In addition, destroyers and cruisers capable of ballistic missile defense will also be sent to the Middle East and the Mediterranean Sea. The statement does not say which warships have been sent, but two US destroyers in the eastern Mediterranean Sea took part in intercepting the barrage of strikes Iran launched against Israel in April.

Austin also ordered the deployment of a fighter squadron to the region, Singh said.

The US already has the USS Wasp amphibious assault ship in the region, which operates with the 24th Marine Expeditionary Unit, capable of carrying out an evacuation of US citizens in Lebanon should it be ordered.

“The United States’ global defense is dynamic and the Department of Defense retains the capability to deploy on short notice to meet evolving national security threats,” Singh said in the statement.

Iran has vowed to attack Israel for the assassination of Hamas political leader Ismail Haniyeh in Tehran. Israel has not commented on the killing.

US officials said the anticipated Iranian attack could occur in the coming days, and the US is closely watching the region for any indications of how it might play out. Officials said the attack may be similar to the barrage of ballistic missiles and drones Iran launched against Israel in April, but it could also be larger and more complex, coordinated with Iranian proxies in the region.

Hezbollah leader Hassan Nasrallah hinted that a coordinated attack on Israel could be in the works after Israel assassinated one of the Iran-backed group’s top commanders in Beirut less than 24 hours before the killing of Haniyeh.

“Because they have picked a fight with everyone, they don’t know where the response will come from … the response will come separately or coordinated,” he said in a speech Thursday.