Bulgaria Accuses Russia of Airspace "Provocation"

Yes...I know....assuming ANYTHING one reads in what modern journalism has become....we do that at our peril !

I am puzzled. IF what I've read in modern news sources is correct - the Russian military is running around in international air space with their transponders off.

If that is true, it would seem appropriate ( since Russia is a member of ICAO) that a complaint should follow with ICAO ?

Does anyone know what kind of transponders the Russians use ? Something like our Mode "C"? Do they use ADS B ?