Swedish corvette HMS Stockholm patrols Jungfrufjarden in the Stockholm archipelago, in Sweden.Anders Wiklund/AP

Last Thursday, Swedish intelligence agents intercepted an "emergency radio call" in Russian. The next day, another radio transmission was heard and a "foreign vessel" was seen in Swedish waters. Ever since, the Swedish military has been on a wild submarine chase, coordinating both naval and air forces to find this mysterious vessel in the Baltic Sea.

While this only became public knowledge last week, the Swedish military revealed over the weekend that it had been "monitoring suspicious activity in the area for several years." The transmissions were reportedly sent to the Russian enclave of Kaliningrad, located between Poland and Lithuania. Unsurprisingly, a Russian official says he has no idea what Sweden is so worried about; he thinks the vessel is Dutch.

"On Sunday, October 19, the Russian Defense Ministry provided assistance wherever possible to the Swedes in their unsuccessful search, saying that there were no incidents with Russian warships [in the Baltic Sea], including submarines," an anonymous Russian Defense Ministry source told ITAR-TASS. "For easing tension in the Baltic Sea and saving Swedish taxpayers' money, we would advise [Sweden] to request explanations from the Dutch Navy command." The Dutch have denied that they own the mystery vessel.

The Swedish military plans to continue the search for several more days. It is currently looking as far away as 44 miles from Stockholm for the vessel, and all forces are armed.

According to AFP, the public has been barred from coming within six miles of the search and all non-essential air-travel has been halted.

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