Defence chiefs in Romania are investigating claims that one of their MIG 21 fighter planes was struck by an Unidentified Flying Object.
The claims came from a leaked report revealed that the cockpit of the jet was shattered in the collision.
Romanian defence ministry officials have ruled out a collision with "normal" objects such as birds and meteorites.
In the report, Chief investigator Commander Nicolae Grigorie said: 'We can definitely say what this thing was not, but we cannot say what it was.'
The incident was recorded on an in-flight camera as the plane was flying above Transylvania.
Pilot Marin Mitrica was injured slightly but managed to land the plane after the blow.
The collision is still a mystery to defence chiefs, and the investigation has been passed on to the Security Committee of European Air Forces.