Former intelligence officer David Grusch testified to US Congress on Wednesday that authorities are covering up evidence of "non-human" unidentified flying objects.
The Pentagon has denied the claims.
What are Grusch's claims on UFOs?
Grusch told a congressional committee that he "absolutely" believes the government was in possession of unidentified anomalous phenomena (UAP), a term which is used by the Pentagon to refer to UFOs.
"I was informed, in the course of my official duties, of a multi-decade UAP crash retrieval and reverse-engineering program," Grusch said.
"I made the decision, based on the data I collected, to report this information to my superiors and multiple inspectors general, and in effect becoming a whistleblower," he said.
When pressed for details, Grusch said he could not comment because the information is classified.
He said that he personally interviewed people with direct knowledge of non-human craft.
"My testimony is based on information I've been given by individuals with a longstanding track record of legitimacy and service to this country," he said, adding that many of these people had "shared compelling evidence in the form of photography, official documentation and classified oral testimony."
US Representative Tim Burchett supported the idea that the government was concealing information, saying "we're going to uncover the cover-up" at the start of the hearing.
"This is an issue of government transparency. We can't trust a government that does not trust its people," he said.
What did US officials say about the claims?
In a statement, Defense Department spokeswoman Sue Gough said investigators had 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."
National Security Council spokesman John Kirby said that he did not have a position on the issue of whether there is life beyond Earth.
"What we believe is that there are unexplained aerial phenomena that have been cited and reported by pilots — Navy and Air Force," he said. "We don't have the answers about what these phenomena are."
Sean Kirpatrick, the head of the Pentagon's All-domain Anomaly Resolution Office that looks into UAPs, told lawmakers earlier this year that the body had "found no credible evidence thus far of extraterrestrial activity, off-world technology, or objects that defy the known laws of physics."
In May of this year, NASA held its first public meeting on UAPs and called for a more rigorous scientific approach to clarify the origin of hundreds of sightings.
