The Air Force is facing a shortage of drone pilots for the MQ-1 Predator and MQ-9 Reaper drones – aircraft that have been a crucial part of the air campaign against ISIS in Iraq and Syria, Pentagon officials said Monday.

Army Col. Steve Warren, a Pentagon spokesman, declined direct comment on the shortage, first reported by the Daily Beast website, but noted that there was a “very high demand for the capabilities” of the drones as launch vehicles for Hellfire air-to-ground missiles and as ISR (Intelligence Surveillance and Reconnaissance) platforms.

“We’re confident the Air Force will do everything it needs to do to fulfill its Title 10 requirements,” Warren said in a reference to Title 10 of the U.S. Code outlining the roles of the armed forces.

The Daily Beast cited a recent memo from Air Force Gen. Herbert “Hawk” Carlisle, commander of the Air Combat Command (ACC), to Gen. Mark Welsh, Air Force Chief of Staff, warning of the shortage of pilots who fly the drones from consoles mostly at bases in the U.S.

“I am extremely concerned,” Carlisle said, about the shortage of pilots for the remotely piloted aircraft (RPAs), which is the preferred Air Force term for the drones.

“ACC believes we are about to see a perfect storm of increased COCOM (Combatant Commander) demand, accession reductions, and outflow increases that will damage the readiness and combat capability of the MQ-1/9 enterprise for years to come,” the Carlisle memo said.

“ACC will continue to non-concur to increased tasking beyond our FY15 (Fiscal Year 2015) offering and respectfully requests your support in ensuring the combat viability of the MQ-1/9 platform,” Carlisle said.

Air Force spokesmen said there were preparing a response to the Daily Beast report, but would neither confirm nor deny the existence of the Carlisle memo. However, other Pentagon sources confirmed that Welsh was in receipt of the memo.

In recent years, the Air Force has had difficulty filling the ranks of pilots needed to meet the increasing demands for the drone fleet from combatant commanders.

In 2013, the Government Accountability Office reported that the Air Force had recruited 110 drone pilots against a requirement for 179.