NATO fighters assigned to the Baltic Air Policing mission were scrambled to intercept a group of Russian military aircraft as they approached Estonian air space on Tuesday, according to a statement provided by NATO spokesperson Dylan White.

“Two Spanish F-18 jets assigned to NATO’s Baltic Air Policing mission scrambled from Estonia’s Amari Air Base on Tuesday morning to intercept unidentified non-NATO military aircraft near Estonian airspace,” White said.

Finland also scrambled fighters to intercept the same group of aircraft, which turned out to be two MiG-31 fighter jets and an AN-26 military transport plane.  While these types of flights are not uncommon for the Russian military, intercepts of this sort highlight the increasing tensions between Russia and the NATO alliance, particularly in the Baltic region, where many could argue Estonia, Latvia, and Lithuania are the allies most at risk of Russian aggression.

Russia’s military annexation of Crimea in 2014 has prompted increased concern in the Baltic states that one of them could be next, particularly because of Russia’s nearby province of Kaliningrad.  A narrow stretch of territory called the Suwalki Gap, which runs for about 65 miles between Poland and Lithuania abuts the border with Kaliningrad and could potentially be captured to sever land supply routes to the Baltic nations from their NATO allies.

While the Russian aircraft did not violate Estonia’s airspace, the scrambled Spanish F-18s did accidentally cross the border into Finnish airspace.  Although Finland has often contributed to NATO operations, they are not a member of the alliance.

“In handing over the intercept to the Finnish jets, the Spanish jets accidentally entered Finnish airspace. NATO’s Air Command has explained the incident to the Finnish Air Operations Centre to improve future coordination,” White said.

Finland addressed the airspace violation in a statement released on Tuesday, stating only that two Spanish fighters were “suspected of having violated Finland’s airspace on Tuesday morning.”

Finland recently began an initiative that aims to bring Russia, NATO, Sweden and Finland to the table to discuss ways to manage the increasingly heavy air traffic in Baltic airspace.  Finland has seen frequent violations of their airspace by Russian military and even commercial aircraft in recent years, but NATO violations remain uncommon.