Sweden Hunts Suspected Foreign Submarine off Stockholm Coast

The Swedish armed forces announced a military operation in islands off Stockholm late Friday evening following reports of suspicious "foreign underwater activity".

"We have begun an intelligence operation... involving ships, helicopters and several ground units," Commander Jonas Wikstroem told reporters, adding that the operation was based on a tip-off from a "credible source".

Wikstroem did not specify how close the operation was to the Swedish capital but said that the military was informing the public as the area has "heavily trafficked".

In recent months, Swedish media have reported an uptick in Baltic Sea manoeuvres by the Russian air force, including a close encounter between a Swedish spy plane in international airspace off Russia's Baltic Sea coast.

"As the government has said, the situation has deteriorated in the Baltic Sea," Wikstroem said, adding that no weapons had been used in the current operation.

During the Cold War the then-neutral -- and now non-aligned -- Nordic country was regularly on alert following Russian submarine sightings, including one notable case in 1981 when a Soviet U-boat ran aground several miles from a largest naval base.