The disruption of Finland's global positioning system (GPS) signal during recent NATO war games came from Russian territory, the Finnish foreign ministry said on Thursday.
The Kremlin on Monday dismissed an earlier allegation from Finnish Prime Minister Juha Sipila that Russia may have intentionally disrupted the signal during the war games.
Finland's air navigation services earlier this month issued a warning for air traffic due to a large-scale GPS interruption in the north of the country.
Norway had posted a similar warning in its own airspace and also accused Russia.
Finnish authorities are continuing to investigate the matter and the issue is being discussed with the Russian Federation through diplomatic channels, the ministry added in a statement on Thursday.
Finland is not a NATO member but it took part as an ally in NATO's largest exercise in decades which ended on Wednesday.
Forces from 31 countries participated in the games close to Russia, in an area stretching from the Baltic Sea to Iceland.
Finland shares a 1,340 km (833-mile) border and a difficult history with Russia. It has lately developed closer ties with NATO but stopped short of full membership in line with a tradition of avoiding confrontation with its eastern neighbor.