Sweden is investigating a report that a submarine wreck has been discovered in the country’s territorial waters.
The military says it is now studying video footage of the wreck taken by divers off Sweden’s eastern coast.
The divers from Ocean X Team and Ixplorer claim they have found a Russian mini-submarine, pointing to Cyrillic letters on the hull.
Last year, Sweden’s military were engaged in an extensive hunt for a suspected Russian submarine.
Naval vessels and planes were involved in the search in the Stockholm archipelago in October, but the operation was called off after one week.
Russia’s defence ministry has denied any of its ships were involved.
Russia’s annexation of Ukraine’s southern Crimea peninsula last year and Moscow’s continuing support for separatist rebels in Ukraine’s east have fuelled suspicion about its intentions towards other neighbouring states, notably in the Baltic.
The Swedish military says it is too early to say definitively that the wreck is indeed that of a submarine.
Spokesman Jesper Tengroth said on Monday it was better “to come back with facts rather than speculation”, the Associated Press news agency reports.
Earlier, Ocean X said in a statement it had found “a Russian mini-submarine… not far from the Swedish coast”.
The company said the vessel was about 20m (66ft) long and 3.5m wide.
“It is unclear how old the submarine is and how long it has been laying at the sea floor, but the Cyrillic letters on the hull indicates that it is Russian.”
It added that the submarine was “completely intact”, and its hatches were closed.
Ocean X’s Stefan Hogeborn was quoted as saying he feared the crew had not been able to escape when the vessel went down.
One expert quoted in the Swedish press suggested the wreck might be that of a Russian submarine that sank in 1916.