The former head of the Pentagon’s secret UFO-hunting bureau has said he believes “we may not be alone”.

Luis Elizondo’s admission came after declassified footage showed US fighter pilots reacting with astonishment as they observed an unknown aerial object off California in 2014.

The Advanced Aviation Threat Identification Programme ended five years ago, when US defence officials shifted attention and funding to other priorities. Democratic senator Harry Reid led the initial push for funding.

After the Department of Defence admitted the programme’s existence Mr Elizondo said the objects it had observed provided “compelling evidence” to support to the idea that humans are not alone.

He told CNN his team’s role was “from a national security standpoint, [to] identify those things that we see, whether we see them electro-optically, we see them with radar, we see them as eyewitness reports ... and try to ascertain and determine if that information is a potential threat”.

He added: “We found a lot. I think it’s probably been a little bit mischaracterised in some of the social media you see and what people put out. A lot of times, when we don’t have a lot of information, we tend to fills in those gaps with what we think is logical.

“And there’s still, by the way, a lot we really don’t know. I think what’s important is that we have identified some very interesting, anomalous type of aircraft.

“Things that don’t have very obvious flight surfaces, any obvious forms of propulsion, and manoeuvring in ways that include extreme manoeuvrability, beyond, I would submit, the healthy g-forces of a human or anything biological.

“Hypersonic velocities, low observability, positive lift – again, seemingly defying the laws of aerodynamics.”

Some of the craft displayed abilities neither the US nor any other country was able to match “that we are aware of”, Mr Elizondo said.