On Thursday, NATO fighters intercepted one An-12 flying from the mainland Russia to the Russian Kaliningrad region, which was flying according to a pre-filed flight plan and kept radio contact with the regional air traffic control center but its onboard transponder was not switched on.
Later on that day, fighter-jets identified and escorted a Su-34 flying from Kaliningrad to mainland Russia. It did not have a flight and did not use onboard transponder but maintained radio communication with the regional air traffic control center.
The NATO air-policing mission is conducted from Lithuania and Estonia.