Several fighter jets were scrambled after an unidentified plane flew through the airspace of six NATO nations, reports suggest.
The mysterious aircraft was spotted by the Hungarian and Romanian Air Force and flew through Poland, Slovakia, Bulgaria and Lithuania, the Daily Star reported.
Two USAF F-16s, two Romanian F-16s and two Hungarian Gripens were sent to intercept the plane after it failed to respond to radio communications.
The plane eventually landed in Debrecen, Hungary to refuel. It took off again and was later found in a small local airfield in Bulgaria known as the Targovishte Airport.
When the authorities finally reached the plane, the pilot was nowhere to be seen and the aircraft appeared to have been abandoned. The plane's engine was reportedly still warm when officers first arrived on the scene, with the occupants likely making a narrow escape.
Forensic officers were pictured inspecting the plane as part of their investigation.
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Prosecutors in the Bulgarian city of Targovishte have launched an investigation into what happened, according to media outlet Euractiv
Bulgarian Ministry of Defence official Dragomir Zakov insisted that the rogue aircraft at had not been a threat to civillians.
“At no time was the plane a threat to civilian or military infrastructure in Bulgaria," he said.
“It flew at low altitudes, which made difficult the interception for fighter jets, but it was monitored all the time.
“The Ministry of Defense is taking the appropriate actions to establish the circumstances.”
