image copyrightGetty Imagesimage captionThe report was written by a task force set up by the US Department of Defense, known as the Pentagon
The US government has said it has no explanation for dozens of unidentified flying objects seen by military pilots.
A Pentagon report released on Friday says of 144 reports made about the phenomena since 2004, all but one remain unexplained.
It does not rule out the possibility that the objects are extraterrestrial.
Congress demanded the report after the US military reported numerous instance of objects seen moving erratically in the sky.