The Swedish military is investigating video footage that appears to show the wreckage of a Russian submarine off the country's eastern coast. 

Sky News reports that video of the 66-foot vessel was shot by a private company, Ocean X Team. The company said on its website that it was unclear how old the ship was or how long it had been at the bottom of the sea, but added "the Cyrillic letters on the hull indicate that it is Russian."

Stefan Hogeborn, an OceanX diver that made the discovery, told Reuters that the submarine was "completely intact" with "no visible damage to the hull" and the hatches closed.

Swedish Armed Forces spokesman Jesper Tengroth told Sky News the country's military was in no hurry to investigate "because the wreck was not going anywhere", adding it is better "to come back with facts rather than speculation".

Meanwhile, an expert told the Swedish tabloid Expressen that he believed the vessel was a Russian "Catfish" submarine dating from 1916, rather than a more recent model. 

In October of last year, the Swedish Navy said it had detected an underwater intruder in the country's territorial waters. Belief that the mystery visitor was a Russian submarine prompted Sweden's largest military mobilization since the end of the Cold War, but the submarine search proved unsuccessful.

Ocean X said that it would mount another expedition to take a closer look at the wreck in the coming days.