The Swedish military is reported to be hunting the seas around Stockholm for a damaged Russian submarine, as an amateur photographer captured a picture of a submerged object in the water.
Rear Admiral Anders Grenstad said the armed forces had made three separate sightings of "foreign undersea activity" in the past few days, which has seen the launch of a large search operation reminiscent of the Cold War.
Publishing the photo taken by a passerby on Sunday, Grenstad would not confirm to reporters that it featured a submarine or speculate on any of the other sightings.
But he said the hunt, involving several hundred people, began on Friday after information was provided by a "credible source", adding that the region is "of interest to a foreign power".
Grenstad said the military could provide no information about any emergency messages suggesting a Russian mini-submarine had run into trouble in Swedish waters and could be damaged, as reported by the Svenska Dagbladet daily.
Russia has denied any involvement. The Defense Ministry in Moscow said its submarines and ships have been "fulfilling their tasks in the world's oceans," according to plan, Russian news agencies reported.
"There have been no emergencies or accidents with Russian military vessels," an unnamed spokesman at the ministry was quoted as saying.
Anders Nordin from the Swedish Maritime Administration said a Russian-owned oil tanker, Concord, which had reportedly been circling near Swedish waters for days, started sailing in a northeasterly direction toward Russia on Sunday morning. But it suddenly turned around and headed back in the direction of Sweden, according to Marine Traffic, a website which monitors vessels in the Baltic Sea.
Media reports said the movements of the Liberian-flagged tanker might be connected to the submarine search.
In 1981, a Soviet sub carrying nuclear weapons was stranded off Sweden's southeastern coast, causing an 11-day diplomatic standoff before Swedish authorities allowed the submarine to return home.
Swedish officials wouldn't speculate on what foreign power could be behind the suspected intrusion Friday. Last month, the Foreign Ministry summoned the Russian ambassador to protest a violation of Swedish airspace by two Russian military aircraft.
Additional reporting by AP