A highly awaited US intelligence report on dozens of mysterious unidentified flying object (UFO) sightings said most could not be explained, but did not rule out that some could be alien spacecraft.

The unclassified report said researchers could explain only one of 144 UFO sightings by US government personnel and sources between 2004 and 2021, sightings that often were made during military training activities.

Eighteen of those, some observed from multiple angles, appeared to display unusual movements or flight characteristics that surprised those who saw them, like holding stationary in high winds at high altitude, and moving with extreme speed with no discernable means of propulsion, the report said.

Some of the 144 might be explained by natural or human made objects like birds or drones cluttering a pilot's radar, or natural atmospheric phenomena, the report said.

Others could be secret US defence tests, or unknown advanced technologies created by Russia or China, it said.

Yet others appeared to require more advanced technologies to determine what they are, it said.

The sightings of what the report calls unidentified aerial phenomena (UAP) “probably lack a single explanation,” said the report from the Office of the Director of National Intelligence.

“We currently lack sufficient information in our dataset to attribute incidents to specific explanations.”

The report made no mention of the possibility of — or rule out — that some of the objects sighted could represent extra-terrestrial life.

The military and intelligence community have conducted research on them as a potential threat.

“UAP clearly pose a safety of flight issue and may pose a challenge to US national security,” the report said.

Some could be US rivals' intelligence collection operations or represent other technology so advanced that the United States military has nothing similar.

The report was ordered after more UFO sightings by military pilots became public and pilot and radar videos leaked out showing flying objects behaving strangely with no explanation.

It stressed that pilots and their aircraft are ill-equipped to identify out-of-the-ordinary objects floating around the skies.

The only one of the 144 incidents in the years covered by the report that was explained turned out to be a large deflating balloon.

The nine-page report released on Friday did not discuss any specific incidents.

It was the public version of a more detailed classified version being supplied to the armed services and intelligence committees of Congress.

Mark Warner, chairman of the Senate Intelligence Committee, said the frequency of UFO reports “appears to be increasing” since 2018.

“Today's rather inconclusive report only marks the beginning of efforts to understand and illuminate what is causing these risks to aviation in many areas around the country and the world.,” Warner said in a statement.

“The United States must be able to understand and mitigate threats to our pilots, whether they're from drones or weather balloons or adversary intelligence capabilities,” Warner said.

At the Pentagon, Deputy Secretary of Defense Kathleen Hicks issued a memorandum ordering more systematic reporting of UAPs encountered during military training and testing.

“Incursions into our training ranges and designated airspace pose safety of flight and operations security concerns, and may pose national security challenges,” said Pentagon spokesman John Kirby.

The department “takes reports of incursions — by any aerial object, identified or unidentified — very seriously, and investigates each one,” Kirby said.

Analysts have yet to rule out an extraterrestrial origin, senior US officials told reporters, speaking on condition of anonymity. The report's language avoided explicit mentions of such possibilities.

Asked about potential alien explanations, one of the officials said: “That's not the purpose of the task force, to evaluate any sort of search for extraterrestrial life. [...] That's not what we were charged with doing.

“Of the 144 reports we are dealing with here, we have no clear indications that there is any non-terrestrial explanation for them — but we will go wherever the data takes us,” the senior official added.

Near misses

The study documented 11 UAP near-misses reported by pilots and a small number of cases in which military aircraft “processed radio frequency energy associated with UAP sightings”.

Most reports also described objects that interrupted training or other US military exercises, it stated.

The task force focused on phenomena witnessed first-hand by military aviators, with 80 reports involving detection by multiple sensors, the report said. Most were from the past few years.

The report established five potential explanatory categories: airborne clutter, natural atmospheric phenomena, US government or American industry developmental programmes, foreign adversary systems and a catch-all “other” category.

The senior US official said the findings did not provide any “clear indications” that the UAP are part of a foreign intelligence-collection programme or a major technological advancement by a potential adversary.

The government in recent years has adopted UAP as its term for what commonly are known as “unidentified flying objects,” or UFOs, long associated with the notion of alien spacecraft.

US Senator Marco Rubio was instrumental in commissioning the report, ordered by Congress six months ago as part of broader intelligence legislation.

“For years, the men and women we trust to defend our country reported encounters with unidentified aircraft that had superior capabilities, and for years their concerns were often ignored and ridiculed,” Rubio said.

“This report is an important first step in cataloging these incidents, but it is just a first step.”

After the report's release, the Pentagon announced plans to “formalise” its UAP investigation mission currently handled by the task force.

Mick West, a UFO skeptic and researcher, said the “report points largely at boring explanations, even including birds and balloons, and identified some areas where we need to improve our data gathering”.

It is not the first official US report on UFOs. The US Air Force conducted a previous investigation called Project Blue Book, ended in 1969, that compiled a list of 12,618 sightings, 701 of which involved objects that officially remained “unidentified”.

In 1994, the Air Force said it completed a study to locate records relating to the 1947 “Roswell incident” in New Mexico.

It said materials recovered near Roswell were consistent with a crashed balloon, the military's long-standing explanation, and that no records indicated that there had been the recovery of alien bodies or extraterrestrial materials.