The head of Sweden's domestic intelligence agency says there is "a real and serious threat against the security" of the country, which "has an increased military strategic importance".
Sapo head Anders Thornberg says the agency has "never had a bigger and more complex task," adding that co-operating with others, at home and abroad, is crucial.
Mr Thornberg did not release details today, but in September non-Nato-member Sweden stationed permanent troops on the Baltic Sea island of Gotland.
The move was described as sending a signal after Russia's 2014 annexation of Crimea and its "increasing pressure" in the region.
When presenting the agency's annual report, Mr Thornberg said it had investigated an undisclosed number of cases where people were suspected of giving out classified information to foreign governments.