"We could not conceal our surprise when we heard Bulgarian Defense Minister Nikolay Nenchev saying in his speech on Nova TV that last month had seen the growing number of violations by Russian military planes, which had their ADS-B transponders off, of the Bulgarian zone of responsibility of NATO airspace," the Russian Defense Ministry spokesman said.

MOSCOW, July 25 /TASS/. The Russian Defense Ministry has received no appeals from the Bulgarian Defense Ministry that Russian military planes allegedly violated flight rules in the Bulgarian zone of NATO airspace and is asking it for explanations, Russian Defense Ministry Spokesman Major General Igor Konashenkov said commenting remarks by Bulgarian Defense Minister Nikolay Nenchev at the local NovaTV channel.

"First of all, we, and not only we, would like to have explanations from Mr. Minister how far away from Bulgaria’s air borders the imaginary zone of NATO airspace lies? The planes of Russian Aerospace Forces make planned regular flights over the Black Sea. Their flight routes lie in strict compliance with international rules of using the airspace over neutral waters. Besides, all the planes, which have made the flights recently, including in June, had their ADS-B transponders on," Konashenkov said.

Despite Nenchev’s words, the Russian Defense Ministry has not received any appeals or requests from the Bulgarian Defense Ministry.

"Therefore, prior to speaking into TV cameras about preventive reaction measures, which the Bulgarian Defense Ministry is taking, we would recommend Mr. Minister to check the reports of his subordinates about the real state of things first," the Russian Defense Ministry said.

In an interview with Nova TV given on Sunday, Bulgarian Defense Minister Nikolay Nenchev claimed that Russian military planes had entered the Bulgarian zone of responsibility in the NATO airspace with their transponders off four times over the past week.

Bulgaria demanded explanations from Moscow calling the incident a provocation against Bulgaria and its armed forces. "We are taking preventive measures," the Bulgarian defense minister stressed.