It is "reasonable" to conclude that the U.S. government thinks some unidentified aerial phenomena (UAP) are not human-made, a Harvard astrophysicist has said.

This week, the U.S. government is expected to release a highly anticipated report into the existence of UAPs—essentially UFOs.

Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard's Department of Astronomy, believes the existence of UAPs would not have been revealed to the public if their origins were from China or Russia and posed a national security risk, he wrote in an op-ed for Scientific American magazine.

Loeb added: "Hence, it is reasonable to conclude that the U.S. government believes that some of these objects are not human in origin."

The astrophysicist said this suggests two scenarios: That UAPs are natural phenomena; or that they are "extraterrestrial in origin."

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