A MYSTERY plane has crossed six NATO countries and triggered a swarm of jets before the pilot gung-ho landed and vanished.
The suspicious two-seater was spotted by Hungarian and Romanian Air Forces flying through their airspace and over Poland, Slovakia and Serbia before landing in Bulgaria.
Every one of those countries bar Serbia is a NATO member.
The mystery plane is believed to have taken off from Lithuania and landed in an abandoned airfield in Targovishte, Bulgaria, according to media outlet Euractiv.
Fighter jets including USAF F-16s, two Romanian F-16s and two Hungarian Gripens were scrambled and tracked the 60-year-old two seater's journey after it failed to respond to radio transmissions.
The small Beechcraft plane reportedly landed in a small airport in Debrecen, Hungary, where a group of people got off to refuel before taking off again and narrowly escaping police.
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Bulgarian authorities have launched an investigation into what happened after the pilot and crew vanished after landing at Targovishte Airport, leaving the plane's engine still warm, according to reports.
The airport has been left unused for years and is now reportedly used for agricultural purposes, according to reports.
Bulgarian Ministry of Defence official Dragomir Zakov said the aircraft entered his country’s airspace in the evening of June 8.
He is reported to have said: "At no time was the plane a threat to civilian or military infrastructure in Bulgaria.
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"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."
It comes a matter of weeks after NATO scrambled its jets to intercept two Russian aircraft near the Finnish border with Norway amid heightened tensions in the region.
The Norwegian Air Force intercepted a Mikoyan MiG-31 'Foxhound' and a Sukhoi Su-24 'Fencer' jet near their airspace on May 27.
Tensions between Russia and the Nordic countries have skyrocketed since Finland and Sweden enraged Vladimir Putin by requesting to join NATO on May 18 – almost doubling Russia's border with their feared nemeses overnight.
The Russian warplanes were intercepted by two NATO F-35 jets over the Norwegian Sea before retreating east, the air force said.
The jets were observed outside Finnmark, in Norway's far north, but were never in official Norwegian airspace.
Stine Barclay Gaasland, comms manager in the Norwegian Air Force, said two F35s are always on standby, in what's called the Quick Reaction Alert for NATO.
"In 15 minutes they must be in the air and be ready at all times. It is 24 hours a day, 365 days a year," Gaasland told Norway's TV 2 Nyhetene.
Trespassing into Norwegian airspace could have provoked a "more aggressive action", Gaasland said.
Asked if the incursions were a threat to Norway, she said: "I do not want to say that, because we are used to it happening, and there is nothing illegal in it.
"We pay close attention to all activity in our local areas."
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Some 58 similar identifications prompted 34 scrambled last year, Norway's Armed Forces said.
The Nordic countries submitted their application together and said they were spurred on by Russia's invasion of Ukraine on February 24.
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