Sweden said on Tuesday the wreck of a submarine found off its coast appeared to be a Tsarist-era Russian vessel that collided with a Swedish ship about a century ago.
"We are most likely talking about the Russian submarine the Som (Catfish) which sank after a collision with a Swedish vessel in 1916 during World War I and before the Russian revolution," the Swedish Armed Forces said.
Speculation had been swirling about the origins of the vessel after Swedish divers announced Monday that a submarine had been found about 1.5 nautical miles off the coast of central Sweden.
The announcement came nine months after a high-profile hunt for a mystery submarine in Swedish waters, suspected to be Russian, and some speculated that the divers had chanced upon a modern Russian vessel.
The Swedish military however quashed rumours and said the vessel was old, referring to the design of the submarine and the lettering on the outer shell seen in the pictures of the wreck taken by the divers.
The military added it did not think a full technical analysis was necessary.
Experts identified it as an Imperial Russian Navy sub that sank with an 18-member crew in May 1916 after a collision with a Swedish vessel.
'Immortalise the memory'
Russian experts have identified the vessel as a Som class submarine, built for the Imperial Russian Navy in 1904 and integrated into the Baltic fleet.
"This is clearly the Som, judging by its location and design," submarine expert Andrei Nikolayev told AFP.
He said the find was very important for Russia.
"As they say, the war is not over until the last soldier has been buried," said Nikolayev, who himself served on submarines.
He said there were several theories as to why the submarine had sunk, adding that its commander was inexperienced.
"A lieutenant was in charge of our submarine," he said.
Konstantin Bogdanov, head of a state-backed team of wreck divers in Russia, also said that the discovery appeared to be the Som, offering his team's help to study the find together with the Swedish divers.
"We are ready to conduct a joint expedition," he said, stressing that it would be important to "immortalise the memory" of those who perished.
Finding the remains of a submarine is more difficult than locating a sunken ship, Bogdanov said, stressing that the latest discovery was a rare occurence.
Last year Bogdanov's team helped Estonian divers identify a wreck in the Baltic Sea as the Tsarist-era Russian submarine known as The Shark (Akula).
Stefan Hogeborn, a diver with the Ocean X Team that made the discovery, said the mini-sub was "completely intact" with "no visible damage to the hull" and the hatches were closed.
"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 indicate that it is Russian," he said in a statement on Monday.
Ocean X Team said the vessel was around 20 metres (66 feet) long and 3.5 metres wide (11.5 feet), adding it was planning a new expedition to study the wreck more closely.
In October, Sweden's navy launched a massive hunt for a foreign submarine, suspected to be Russian, in the Stockholm archipelago.
The military subsequently confirmed that "a mini-submarine" had violated its territorial waters, but was never able to establish the vessel's nationality.
Last year's hunt for the mystery vessel came at a time of particularly high tensions between Russia and the West over the conflict in Ukraine.