The U.S. is preparing to send more combat aircraft to the Middle East, officials say.

The United States is preparing to send additional combat aircraft to the Middle East in response to threats from Iran and its proxies in Gaza, Lebanon and Yemen to attack Israel in the coming days to avenge the death of Ismail Haniyeh this week, American officials said on Friday.

One U.S. military official, speaking on condition of anonymity to discuss operational matters, said that American forces in the Middle East were taking “necessary measures” to increase combat readiness and to protect U.S. troops and allies against any threats from Iran or Iran-backed militia groups.

How many planes to send is still being worked out, as are final approvals from senior officials including Defense Secretary Lloyd J. Austin III. Officials said they were seeking to calibrate the American response to send enough of the right types of aircraft as quickly as possible to help defend Israel without appearing to escalate the conflict.

Any additional air power could be crucial. Iran fired more than 300 drones and missiles against Israel in a major attack in April, but only a handful got through, causing only slight damage. U.S. Air Force jets based in Jordan and in Saudi Arabia coordinated with French, Jordanian and British Air Force fighters to shoot down more than 80 drones.

Iran telegraphed that strike in advance, giving the Pentagon sufficient time to move additional combat aircraft and Navy ships into place while U.S. commanders negotiated access to airspace for fighter jets to operate in and coordinated air defense batteries on the ground to help defend Israel.

It’s unclear whether Israel and its allies will have that much time to prepare for any new round of major Iranian attacks, officials said.