Swedish naval ships, helicopters and troops on the ground have expanded their search for what they believe is a foreign submarine in distress not far from their coast.
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The search has entered its fifth day.
Before the Cold War thaw, there were instances when Sweden discovered Russian subs illegally prowling its waters, but Russia has denied that the mystery sub is one of theirs. Instead, it has claimed that the vessel is a Dutch submarine.
The alleged submarine has been spotted at least three times since Friday in various parts of the Stockholm archipelago. One spotting placed the vessel approximately 12 nautical miles from the country's capital.
The most worrisome question about the mystery sub is whether or not it is carrying nuclear weapons.
According to The Associated Press, there was an incident in 1981 where a Soviet submarine carrying such weapons was stranded off Sweden's southeastern coast.
Russian officials are claiming that the submarine is a Dutch sub that was in the area for planned exercises with the Swedish military, but both Swedish and Dutch officials said that the submarine cited by the Russians has been in Estonia since Friday morning.
Swedish government officials aren't the only ones concerned about a possible return to Cold War tactics, especially in light of heightened tensions in the Ukraine.
Latvian Foreign Minister Edgards Rinkevics writing on Twitter that he is "closely following" the situation and believes it "may become a game changer of the security in the whole Baltic Sea region."
The Associated Press contributed to this report.