Sweden has reportedly launched a secret submarine hunt off the Stockholm coast, after reports of a possible submarine conning tower in Swedish waters.

Swedish Armed Forces spokesman Philip Simon was quoted by the Dagens Nyheter newspaper as saying: "We consider the informant to be very credible.

"We had ships and ground units nearby, so we were able to quickly respond to that observation. Unfortunately, it did not yield any results."

"We consider the informant to be very credible."

The informant, who has extensive military experience, added that the alleged submarine, spotted near the Stora Hoggarn Island located in the north-east of Stockholm, was moving towards the capital.

Commenting on the photograph of the possible submarine, Dagens Nyheter’s military sources noted: "It looks like a black submarine tower.

"You can also see several other ships that operate normally in the waters, such as the Finland ferries."

On 17 October, Sweden deployed helicopters, minesweepers and approximately 200 service personnel to search for suspicious foreign underwater activity off the Stockholm coast.

The activity was reported to be a submarine, a mini-submarine or divers, possibly with some sort of underwater vehicle.