NATO member Estonia said Thursday that a Russian air force plane violated its airspace in what the Baltic nation alleged was the sixth such incident this year by a Russian aircraft.
The alleged intrusion took place at noon Wednesday as the Beriev A-50 plane entered Estonia's airspace near the Baltic Sea island of Vaindloo and stayed there for less than one minute, Estonia's military said in a statement.
It added that the Russian plane's crew had presented a flight plan but failed to maintain radio contact with Estonian Air Navigation Services and had the plane's transponder switched off.
Estonia's Foreign Ministry summoned Russian Ambassador Alexander Petrov to protest and gave him a note for Moscow about what it called a "very unfortunate and serious incident."
"Such a series of repeated violations (by Russian aircraft) is by no means acceptable," the Estonian ministry added.
Download the NBC News app for breaking news and politics
Vaindloo, a small island that belongs to Estonia, is near a corridor where Russian planes fly from the St. Petersburg area to Kaliningrad, Russia's Baltic Sea exclave located between Poland and Lithuania.
European Union member Estonia has recorded numerous air violations by Russian aircraft — civilian and military — in past years and made repeated protests to Moscow.
Relations between Estonia and neighboring Russia have remained icy since the collapse of the Soviet Union. The two countries have yet to ratify a border treaty 30 years after Estonia, a former Soviet republic, regained its independence in August 1991.