A Russian oil tanker sailing under a Liberian flag has been spotted zig-zagging off the Swedish coast near Stockholm despite having Denmark as its listed destination, Ritzau reports.
The picture in the tweet below shows the ship's movements since October 15th.
Swedish newspaper Svenska Dagbladet reported that Swedish intelligence officials intercepted encrypted messages relayed between transmitters in the Stockholm archipelago and the Russian exclave Kaliningrad.
An underwater craft in distress can be difficult to manoeuvre, which might explain why it was spotted above the waterline, the newspaper said.
A damaged submarine would also need help from a support vessel, Svenska Dagbladet said, leading to the suspicion that the Russian-owned oil tanker NS Concord could be in the area to serve as a supply ship.
More than 200 troops, Swedish stealth ships, minesweepers and helicopters have been searching an area of the Baltic Sea about 50 kilometres east of the Swedish capital since Friday evening after reports of possible foreign underwater activity.