The report, submitted to Congress and released to the public, encompasses 144 observations of what the government officially refers to as "unidentified aerial phenomenon," or UAP, dating back to 2004. It was issued by the Office of the Director of National Intelligence in conjunction with a U.S. Navy-led UAP task force.
"UAP clearly pose a safety of flight issue and may pose a challenge to U.S. national security," the report stated, adding that the phenomena "probably lack a single explanation."
"In a limited number of incidents, UAP reportedly appeared to exhibit unusual flight characteristics. These observations could be the result of sensor errors, spoofing, or observer misperception and require additional rigorous analysis," it added.
The report includes some UAP cases that previously came to light in the Pentagon's release of video from U.S. naval aviators showing enigmatic aircraft off the U.S. East and West Coasts exhibiting speed and maneuverability exceeding known aviation technologies and lacking any visible means of propulsion or flight-control surfaces.
A senior U.S. official, asked about the possibility of extraterrestrial explanations for the observations, 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 official added.
The report established five potential explanatory categories: airborne clutter, natural atmospheric phenomena, U.S. government or American industry developmental programs, foreign adversary systems and a catch-all "other" category.
All but one of the incidents, an instance attributed to "airborne clutter," remain unexplained, subject to further analysis, U.S. officials, speaking on condition of anonymity, told reporters during a briefing describing the report's findings.
For the remaining 143 cases, the government has yet to rule in or out whether the sightings might be of extraterrestrial origin, the officials said.
"Of data we have, we don't have any clear indications that any of these unidentified aerial phenomena are part of a foreign (intelligence) collection program, and we don't have any clear data that is indicative of a major technological advancement by a potential adversary," the senior official said.
The government in recent years has adopted UAP as its preferred term for what are otherwise known as "unidentified flying objects," or UFOs, long associated with the notion of alien spacecraft.
A second senior official said that 21 of the reports show UAPs "that appear to have some sort of advanced propulsion or advanced technology," and appear to lack any means of propulsion or acceleration and exhibit speeds beyond what the United States believes foreign adversaries possess.
The report was ordered by Congress as part of broader intelligence legislation signed by former President Donald Trump in December. Senator Marco Rubio was instrumental in commissioning it.
"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."
The report marks a turning point for the U.S. government after the military spent decades deflecting, debunking and discrediting observations of unidentified flying objects and "flying saucers" backing back to the 1940s.
"Anytime there is a safety-of-flight or counterintelligence concern we take those things very seriously and we will continue to take those things seriously," the first senior official said.
U.S. Representative Adam Schiff, chairman of the House of Representatives Intelligence Committee, urged a systematic analysis of the potential national security and flight safety risks posed by UAP "without preconceptions" to determine whether they are the result of a foreign adversary, atmospheric or other aerial phenomena, space debris "or something else entirely."
It is not the first official U.S. government report on the subject. For example, the U.S. Air Force carried out a previous UFO investigation called Project Blue Book https://www.archives.gov/research/military/air-force/ufos#geninfo, 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 announced that it had 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.