The US is concealing a longstanding programme that retrieves and reverse engineers unidentified flying objects, a former Air Force intelligence officer testified Wednesday to Congress. The Pentagon has denied his claims.

Retired Maj. David Grusch's highly anticipated testimony before a House Oversight subcommittee was Congress' latest foray into the world of UAPs or unidentified aerial phenomena," which is the official term the US government uses instead of UFOs.

While the study of mysterious aircraft or objects often evokes talk of aliens and little green men, Democrats and Republicans in recent years have pushed for more research as a national security matter due to concerns that sightings observed by pilots may be tied to US adversaries.

Grusch said he was asked in 2019 by the head of a government task force on UAPs to identify all highly classified programs relating to the task force's mission. At the time, Grusch was detailed to the National Reconnaissance Office, the agency that operates US spy satellites. I was informed in the course of my official duties of a multi-decade UAP crash retrieval and reverse engineering program to which I was denied access, he said.

Asked whether the US government had information about extraterrestrial life, Grusch said the US likely has been aware of non-human activity since the 1930s. The Pentagon has denied Grusch's claims of a coverup. In a statement, Defence Department spokeswoman Sue Gough said investigators have not discovered any verifiable information to substantiate claims that any programs regarding the possession or reverse-engineering of extraterrestrial materials have existed in the past or exist currently. The statement did not address UFOs that are not suspected of being extraterrestrial objects.

Grusch says he became a government whistleblower after his discovery and has faced retaliation for coming forward. He declined to be more specific about the retaliatory tactics, citing an ongoing investigation. It was very brutal and very unfortunate, some of the tactics they used to hurt me both professionally and personally, he said.

Rep. Glenn Grothman, R-Wis., chaired the panel's hearing and joked to a packed audience, Welcome to the most exciting subcommittee in Congress this week. But members of both parties asked Grusch about his study of UFOs and the consequences he faced. I take it that you're arguing what we need is real transparency and reporting systems so we can get some clarity on what's going on out there, said Rep. Jamie Raskin, D-Md.

Some lawmakers criticized the Pentagon for not providing more details in a classified briefing or releasing images that could be shown to the public. In previous hearings, Pentagon officials showed a video taken from an F-18 military plane that showed an image of one balloon-like shape. Pentagon officials in December said they had received several hundreds of new reports since launching a renewed effort to investigate reports of UFOs.

At that point, we have not seen anything, and we're still very early on, that would lead us to believe that any of the objects that we have seen are of alien origin, said Ronald Moultrie, the undersecretary of defence for intelligence and security. Any unauthorised system in our airspace we deem as a threat to safety.