WASHINGTON (AFP) - Are aliens watching us? That is what Americans hope to find out when a report on the United States government's secret files on unidentified flying objects (UFOs) goes to Congress next month after years of sightings and videos suggesting that highly advanced extraterrestrials are, indeed, out there.
But the report from the Director of National Intelligence, pulled together with classified military files, could fall short of explaining scores of purported UFO incidents over decades.
While not clearly rejecting the alien theory, Pentagon officials make clear their real interest is in whether UFOs, or unidentified aerial phenomena (UAP) in the US military's parlance, could represent actual threats from adversaries here on earth.
Attention has mounted ahead of the report that the US spy chief is required to turn over to Congress by the end of next month.
An unclassified version will be made public, while a more detailed classified one will remain secret - likely frustrating hard-core "ufologists".
The CBS news journal "60 Minutes" interviewed US Navy pilots who said they had seen inexplicable aircraft that flew faster and were more manoeuvrable than anything seen before.
Officials with access to classified intelligence drummed up the mystery.
"What is true - and I'm actually being serious here - is that there's footage and records of objects in the skies that we don't know exactly what they are," former president Barack Obama told "The Late Late Show" on May 17.
"There are a lot more sightings than have been made public," Mr John Ratcliffe, who was director of national intelligence for the last eight months of former president Donald Trump's administration, said on Fox News in March.
"There are instances where we don't have good explanations for some of the things that we've seen."
Last year, the US Defence Department released three black-and-white videos taken by navy aviators that appear to show UFOs.
The pilots express amazement at what they are seeing, and no explanation is offered.
For the department, though, it is not about aliens but about possible technology created by US rivals that they were unaware of.
In August, the Pentagon formed a task force "to detect, analyse and catalogue UAPs that could potentially pose a threat to US national security".
But the military does not want to reveal the results of its internal investigations because it hopes to protect its own activities, technology and intelligence.
If UAPs are from a potential adversary, the task force does not want to provide information that would give them details on what is known or unknown, a Pentagon official said.
That leaves many incidents "unexplained", at least to the public.
The official did say, however, that many UFO sightings can be everyday objects that increasingly clutter air space: weather balloons, metallic party balloons, amateur and professional drones, all with varying radar signatures.
In addition, there are many variables that affect what pilots think they are seeing: their own speed, reflections from the sun, the weather and other issues.
A pilot over the ocean might think an object is moving with extreme speed because it appears that way, and in reality it is moving as slowly as a car.
Moreover, sightings could also be of the Pentagon's own highly classified experiments and prototypes.
"The Department of Defence takes reports of incursions into our airspace - by any aircraft, identified or unidentified - very seriously, and investigates each one," said Ms Sue Gough, a Department of Defence spokesman.
"As we collect additional data, we expect to close the gap between identified and unidentified and avoid strategic surprise regarding adversary technology," she said.
The worry is that at least some of the incidents could represent technology that the US does not have, but that China or Russia might possess.
"If somebody is up there trying to identify how we train and how we fight, that gives them an advantage," said the Pentagon official.
Mr Luis Elizondo, who worked in the Pentagon investigating UFOs, said on the ABC News programme "This Week" on Sunday that some of the objects that have been sighted "can outperform anything that we have in our inventory".
He said: "We know that whatever it is in our skies is real. The question is, what is it? The bottom line is, we simply don't know."