A Mexican congressional hearing where two alleged "non-human" alien corpses were displayed has been described as an "unsubstantiated stunt".

The mummified specimens were displayed in glass cases during a hearing at Mexico's Congress.

Ryan Graves, a former US Navy pilot who in July claimed the number of UFOs or UAPs (unidentified anomalous phenomena) was being "grossly underreported", was at the meeting.

However, he was less than complimentary of the proceedings.

"Unfortunately, yesterday's demonstration was a huge step backwards for this issue," he posted on X, formerly known as Twitter.

"My testimony centered on sharing my experience and the UAP reports I hear from commercial and military aircrew through ASA's witness program.

"I will continue to raise awareness of UAP as an urgent matter of aerospace safety, national security, and science, but I am deeply disappointed by this unsubstantiated stunt."

The Mexican politicians were told the specimens were found in the city of Cusco, Peru, and were estimated to be 1,000 years old.

Journalist and UFO researcher Jaime Maussan testified under oath that almost a third of their DNA is "unknown" and the specimens were not part of "our terrestrial evolution", Mexican media reported.

"They are not beings recovered from a UFO crash," he said.

"Instead, they were found in diatom (algae) mines and subsequently became fossilised."

Mr Maussan told the Mexico City delegation the specimens had been examined at the Autonomous National University of Mexico.

He said scientists used radiocarbon dating to gather DNA evidence and X-rays had shown one to have "eggs" inside.

However, physicist and presenter professor Brian Cox said the specimens were unlikely to be aliens.

"They are way too humanoid," he posted on X.

"It's very unlikely that an intelligent species that evolved on another planet would look like us.

"Secondly - send a sample off to 23andme - let alone the university down the road - and they'll tell you within 10 minutes."

Last year marked the 75th anniversary of the Roswell UFO incident, which still attracts theories to this day.

An extra-terrestrial spacecraft is said to have crashed in the desert of New Mexico in 1947, leading to the possible recovery of alien bodies which theorists claim has been covered up by the American government.