In this image made available by 331/332 Squadron of the Norwegian Air Force a Russian TU-95 Bear H flies over International waters off the coast of Norway on Friday Aug. 17, 2007. Eleven Russian military planes exercised West of Norway ... more >

A Russian spy plane briefly entered NATO airspace Tuesday, the first reported incident of a Russian military aircraft encroaching on territory patrolled by the alliance since the Ukraine crisis began.

The spy plane entered Estonian airspace near the island of Saaremaa for a period of less than one minute after NATO fighter jets steered the plane away from Denmark, NATO spokesman Lt. Col. Jay Janzen said.

NATO officials identified the spy plane as a Russian Ilyushin-20, which was designed to gather intelligence, Lt. Col. Janzen said. Officials tracked the spy plane from its launching point from the Russian seaport city of Kaliningrad and watched it kind of doing a circuit around the Baltic before the aircraft headed into Estonia airspace, he said.

NATO increased its policing efforts in the Baltic Sea region this year in response to concern among NATO allies like Estonia, Latvia and Lithuania when Russia annexed a peninsula in southern Ukraine.

Lt. Col. Janzen said the incursion, while brief and relatively minor, was the first since a conflict over Russias aggressive behavior in Ukraine strained relations between Moscow and the alliance.

Since the Ukraine crisis started, there havent been any incursions into the areas that NATO patrols as part of its air policing mission. This was the first one, he said.

Estonias Foreign Ministry spokeswoman Mari-Liis Valter said Wednesday that Estonia considers the violation serious and demands an explanation for why the spy plane entered its airspace, according to the Associated Press.

Estonias ministry of foreign affairs summoned the Russian ambassador Wednesday and presented him with a diplomatic note of protest, according to Embassy of Estonia spokeswoman Maria Belovas.

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Russian spy plane encroaches on NATO-patrolled airspace