Barack Obama says a secretive US base isn’t holding extraterrestrials - unless a massive conspiracy kept him in the dark.

Former US President Barack Obama said he’s seen no evidence that aliens have made contact with Earth, clarifying his position on extraterrestrials after comments he made in a podcast went viral.

"I saw no evidence during my presidency that extraterrestrials have made contact with us," Obama clarified on social media.

UC San Diego is participating in the federal DHS program Operation Stonegarden at a time of heightened Border Patrol immigration enforcement.