European leaders are sounding the alarm about so-called hybrid Russian warfare over confirmed and suspected aerial incursions in recent weeks in several countries.

Russian drones have entered Polish and Romanian airspace, Russian fighter jets have entered Estonian airspace, a Russian jet flew over a German Navy frigate in the Baltic Sea, airports in Denmark and Norway had to shut down temporarily due to unknown drone activity, and Germany is investigating whether Russia was responsible for a mysterious swarm of drones caught spying on a power plant, hospital, and shipyard — all within the last month.