Bulgarian Defense Minister Nikolay Nenchev said on Sunday an increased number of violations of the country's airspace by Russian military aircraft had been observed over the past weeks.
"Our fighter jets are ready to intercept them," he told private national NOVA TV broadcaster.
At least ten cases of violation have been recorded over the past ten months, according to Nenchev.
The development constitutes "provocation toward Bulgaria and its Air Force," in his words.
The aircraft had turned off their transponders that allow for them to be more easily located.
The frequent need scramble jets, however, brings additional expenses to the ministry, he made clear.
There has been no official comment from the Foreign Ministry in Moscow as of Monday afternoon.
Bulgaria last year repeatedly denied Russian aircraft, supposedly carrying humanitarian aid for Syria, to fly over its territory, in a move that drew anger from Moscow.
50% more Chinese Tourists in Bulgaria
Potentially Defective Aluminum was used by All Car Manufacturers in Japan