"Non-human biologics" were recovered by the US government from crash sites, according to a former US intelligence official.
David Grusch said he was "absolutely" certain the US government is in possession of non-human vehicles.
Asked at a Congress hearing on UFOs whether the "pilots who piloted this craft" were also found, he said "biologics came with some of the recoveries, yeah".
He was then asked if the biologics were "human or non-human".
"Non-human", he replied, adding: "That was the assessment of people with direct knowledge of the programme I talked to, that are currently still on the programme."
He said he prefers to use the term "non-human" rather than alien or extraterrestrial.
Mr Grusch was giving evidence at a hearing in which an ex-Navy pilot claimed the US government was "hiding crucial information" about UFOs.
British-built satellite Aeolus deliberately crashed into Atlantic in world first
US government 'hiding crucial information' about UFOs, says ex-Navy pilot who claims he saw them
How do huge Jupiter-style planets form? Spectacular new image may have the answer
The session was held by the House Oversight Committee, which covers US national security and foreign affairs.
The hearing was announced last week amid increased attention on reported sightings of UFOs - officially known as unidentified aerial phenomena or UAPs.
Mr Grusch, who said he has not personally spotted a UAP, told the panel that he...
When a company promises to save the planet by 2050, it sounds reassuring. But what if that promise comes with no real plan, no credible evidence, and no accountability? A sweeping new study reveal...