Russia has been stockpiling "jet-powered drones," a new model of long-range strike drones that fly faster and are harder to intercept.

Kaliningrad has long been a source of tension between Russia and Nato, given its strategic location on the Baltic Sea, and the potential for Russia to cut off the three Baltic states from the rest of their Nato allies if they were to annex a land corridor between the exclave and its military ally Belarus.