NATO has reported an "unusual" spike in Russian military flights over the Black, Baltic and North seas and the Atlantic Ocean during the past two days.

NATO military spokesman Jay Janzen said Wednesday that four groups made up of Tu-95 Bear H strategic bombers, MiG-31 fighters and other Russian warplanes have been conducting large-scale maneuvers in international airspace. He said Norwegian, British, Portuguese, German and Turkish fighters have been scrambled in response.

No incidents were reported, but Janzen said the flights were unusual by their scale. He said NATO was still tracking some of the Russian aircraft as of mid-afternoon Wednesday.

Tensions have been running high between NATO and Russia since Russia annexed the Crimean Peninsula from Ukraine in March.