A new report from U.S. intelligence officials claims that there's no evidence that the unidentified flying objects (UFOs) sighted in recent years — even objects that seemed to perform aerodynamic feats beyond the capabilities of human aircraft — are extraterrestrial in origin.

But the objects aren't American-made technologies, either, officials said in the report. In that case, what are these UFOs? It's hard to say with certainty, as many of the likeliest explanations — weather balloons or other airborne experiments, for instance — are contradicted by the unusual speed or maneuverability of the objects, according to the report.

These and other assessments of unexplained sightings were included in a long-awaited Pentagon document on UFOs that has not yet been released, The New York Times reported June 3, citing "senior administration officials" who were briefed on the report's findings.

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The report is scheduled for presentation to Congress by June 25, and most of it will then be made available to the public, the Times reported. However, the government is keeping parts of the report classified, though this portion of the document "will not contain any evidence concluding that the phenomena are alien spacecraft," according to the Times.

In the report, officials examined more than 120 incidents describing UFOs, spanning two decades. Many of these sightings involved U.S. Navy personnel, the Times reported. One possible explanation for some of these UFOs — and a source of concern for military officials and intelligence agencies — is that the mysterious craft are examples of hypersonic technology developed in China or Russia, the Times reported.

On Dec. 21, 2020, the U.S. Senate Intelligence Committee gave the director of national intelligence and the secretary of defense 180 days to produce a report on UFOs documenting sightings and proposing new standards for recording and interpreting such incidents, Live Science previously reported.

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In recent years, U.S. Navy pilots captured and shared footage of mysterious objects seemingly flying at hypersonic speeds without visible means of propulsion. This footage reignited a long-standing American fascination with UFOs that was sparked in 1947 by rumors of a "flying saucer" spotted in U.S. airspace and the subsequent launch of the U.S. Air Force's UFO-investigating Project Blue Book, according to the National Archives Foundation.

More recently, on May 14, a filmmaker who produces UFO documentaries shared footage of a spherical UFO that "the U.S. Navy photographed and filmed" as it hovered over the ocean and then dove beneath the waves. A Pentagon spokesperson confirmed that U.S. Navy personnel did capture the footage but provided no further information about the object, Live Science previously reported.

Originally published on Live Science.