[BBC] Sweden could use force in its search for a suspected foreign submarine, a senior Swedish naval officer has told the BBC.Real Admiral Anders Grenstad said if a submarine were discovered, weapons could be used to make it surface.
But the military operation is focused on gathering intelligence, he added.
Russia has denied suggestions that one of its submarines got into trouble near Stockholm last week after distress signals were reportedly intercepted.
There have been several reported sightings of a mysterious vessel off the Swedish coast, prompting the search operation.
Rear Admiral Grenstad, who is deputy chief of joint operations in the search, said he had "no clue" which country owned it.
"Everybody is speculating - that's what you get when you're hunting submarines," he added.