A US fighter pilot who was rescued after being shot down over Iran has described witnessing something extraordinary moments before ejecting from his aircraft.

The F-15 pilot revealed that prior to ejecting to safety, he observed multiple Iranian drones suspended in the air, moving in unison, in a formation that bore a striking resemblance to a jellyfish, according to four sources familiar with the matter.

Such a scene has never previously been reported, and was relayed by the pilot to intelligence officials during a debriefing following the incident back in April.

According to CNN, the revelation immediately ignited a fierce debate within the US intelligence community that has yet to be resolved.

Should the pilot's account prove accurate, it would signal a deeply alarming and extraordinary leap forward in Iranian drone capabilities.

"Multiple drones interconnected and moving as one with smaller drones below the bigger drones like legs," one of the sources familiar with the pilot's witness account told CNN. "Real alien sh*t."

A second source told CNN the pilot described witnessing a "minefield of drones" in the air.

Two sources disclosed to CNN that while the precise cause of the F-15 downing remains under investigation, initial reports suggested the drone formation may have enabled Iran to bring down the US jet.

The downing of the F-15, which carried both the pilot and a weapons system officer, marked the first occasion a US aircraft has been shot down over Iran during the conflict.

According to CNN, American intelligence officials have been divided over how to interpret the pilot's account of what he witnessed.

Some argued that he had suffered concussion in the crash. Furthermore, it was the second occasion he had been shot out of the sky during the Iran war, having previously been among the pilots brought down in a friendly fire incident by Kuwaiti forces, sources revealed.

One source disclosed that during the briefing, intelligence officials subjected him to intense questioning, asking, "Are you sure you saw what you are saying you saw?"

The US Air Force redirected enquiries to US Central Command, which failed to directly address questions from CNN. The Office of the Director of National Intelligence did not respond to a request for comment.

The disclosure comes just days after the US signed a memorandum of understanding that establishes a framework for bringing the war to an end. Last weekend, Vance and other senior US officials participated in negotiations with Iranian officials in Switzerland.