Russia is being blamed for disrupting GPS signals over Scandinavia during a large-scale NATO exercise.
The claim comes less than a week after NATO forces ended Trident Juncture, which simulated an invasion of Norway and how Alliance forces would respond.
Operations took place in Norway, parts of Finland and Sweden and involved 50,000 troops, 250 aircraft and 10,000 tanks.
NATO Secretary General Jens Stoltenberg declined to confirm or deny suggestions of Russian interference.
At a news conference in Berlin he said would he not "point at any specific nation now".
"I will just says we have increased our abilities to deal with this kind of challenges and threats including during military operations."
Pilots in Finland and Norway are reported to have lost GPS navigation signals over parts of the drill near Russia's western border.
Finland's Prime Minister said Moscow was likely to blame for the jamming and an investigation is underway.
Russia has effectively denied disrupting the NATO exercise, saying it had “no information” about the claim.