(CNN) -- There are fears of Russians and it is October, but it's not a Tom Clancy novel. It is a case of international naval intrigue off the Swedish coast that brings back memories of the Cold War. The Swedish military on Monday intensified a search in the ocean off Stockholm for an underwater mystery vessel, but stopped short of calling it a submarine. Civilian vessels were ordered to stay at least six miles (about 10 kilometers) away from the Swedish warship conducting the search, the English-language website The Local reported. The search began Thursday after Swedish intelligence picked up an emergency radio call in Russian, reported The Local, citing the Swedish newspaper Svenska Dagbladet. The radio transmissions were being sent to the Russian enclave of Kaliningrad, 330 miles (530 kilometers) south of Stockholm on the Baltic's southern shore, according to The Local report. There were also reports that a foreign vessel was spotted in the waters near Stockholm. Russia on Sunday denied it has any vessel in Swedish waters. Moscow suggested the vessel may belong to the Netherlands and have been involved in naval exercises off Sweden, according to a report from Russia's Itar-TASS news agency. The Dutch were quick to respond, saying a sub involved in the exercises was anchored in Tallinn harbor of NATO-ally Estonia for the weekend, according to a report from Agence France-Presse. 'We have good stamina' On Monday, the Swedish military vowed to continue searching at least for the next few days, according to The Local. "We have good stamina," The Local quoted defense spokesman Dag Enander. "We're using the sensors we have and are searching both from land and water," Enander was quoted as saying. To confuse matters even more, the Swedish military said Monday that it purposely provided incorrect information on Sunday about where the mystery vessel was sighted to keep the search area secure. U.S. officials told CNN there are no U.S. submarines or surface ships in the immediate area. U.S. intelligence doesn't know of any Russian assets in that area, the officials said. All the activity begs the question, why would a Russian sub need to snoop around in Swedish waters anyway? Johan Wiktorin of the Swedish Royal Academy of War Sciences gave three possibilities to The Local: . "They could be mapping the waters in order to be able to navigate them in the event of hostilities," Wiktorin is quoted as saying. "They could also be installing equipment, like sensors, that could track or get an observation of our units in that area," he goes on. "Or they could also possibly reconnoiter our (defense) systems." Russian military around the world . Whether there is a Russian sub in Swedish waters or not, there is no question that Russian forces have been active in the Baltic and around the globe this year. In fact, the Swedish military said Sunday that it has monitored suspicious activity for several years, according to another report in The Local. In July, a U.S. Air Force reconnaissance plane fled into Swedish airspace after the Russians took the unusual action of beginning to track it with land-based radar. The Russians then sent at least one fighter jet into the sky to intercept the U.S. aircraft. And on April 23, a Russian Su-27 Flanker fighter jet buzzed within 100 feet of the nose of a U.S. Air Force RC-135U reconnaissance plane over the Sea of Okhotsk between Russia and Japan, a Defense Department official said. Also on April 23, Dutch fighter jets scrambled to intercept a pair of Russian Tu-95 Bear bombers that entered a half-mile into Netherlands airspace. On June 4, according to U.S. defense officials, four long-range Russian Tu-95 bombers, accompanied by an aerial refueling tanker, flew into the U.S. Air Defense Identification Zone, an area extending 200 miles (320 kilometers) from the North American coast, off Alaska, where they were intercepted by U.S. F-22 fighter jets. Two of the Russian bombers peeled off and headed west, while the other two flew south and were identified by U.S. F-15 fighters within 50 miles of the California coast. And last month, two Alaskan-based U.S. Air Force F-22 fighter jets intercepted two Russian IL-78 refueling tankers, two Russian MiG-31 fighter jets and two Russian Bear long-range bombers, according to Capt. Jeff Davis of the North American Aerospace Defense Command. More than six hours later, two Canadian CF-18 fighter jets intercepted two Russian bombers in the Beaufort Sea, Davis said. Those Russian planes came within about 40 nautical miles of the Canadian coastline, he said. Earlier this year, a top U.S. Air Force general said Russia was stepping up its military activities in the Asia-Pacific region as tensions increased over Ukraine and Russia's move into Crimea.
Emergency radio call picked up by Swedish military, report says .
Radio transmissions sent to Russian enclave on Baltic Sea, report says .
Russia denies any vessel in Swedish waters .
Russian military has been active around world this year .
(CNN) -- There are fears of Russians and it is October, but it's not a Tom Clancy novel. It is a case of international naval intrigue off the Swedish coast that brings back memories of the Cold War. The Swedish military on Monday intensified a search in the ocean off Stockholm for an underwater mystery vessel, but stopped short of calling it a submarine. Civilian vessels were ordered to stay at least six miles (about 10 kilometers) away from the Swedish warship conducting the search, the English-language website The Local reported. The search began Thursday after Swedish intelligence picked up an emergency radio call in Russian, reported The Local, citing the Swedish newspaper Svenska Dagbladet. The radio transmissions were being sent to the Russian enclave of Kaliningrad, 330 miles (530 kilometers) south of Stockholm on the Baltic's southern shore, according to The Local report. There were also reports that a foreign vessel was spotted in the waters near Stockholm. Russia on Sunday denied it has any vessel in Swedish waters. Moscow suggested the vessel may belong to the Netherlands and have been involved in naval exercises off Sweden, according to a report from Russia's Itar-TASS news agency. The Dutch were quick to respond, saying a sub involved in the exercises was anchored in Tallinn harbor of NATO-ally Estonia for the weekend, according to a report from Agence France-Presse. 'We have good stamina' On Monday, the Swedish military vowed to continue searching at least for the next few days, according to The Local. "We have good stamina," The Local quoted defense spokesman Dag Enander. "We're using the sensors we have and are searching both from land and water," Enander was quoted as saying. To confuse matters even more, the Swedish military said Monday that it purposely provided incorrect information on Sunday about where the mystery vessel was sighted to keep the search area secure. U.S. officials told CNN there are no U.S. submarines or surface ships in the immediate area. U.S. intelligence doesn't know of any Russian assets in that area, the officials said. All the activity begs the question, why would a Russian sub need to snoop around in Swedish waters anyway? Johan Wiktorin of the Swedish Royal Academy of War Sciences gave three possibilities to The Local: . "They could be mapping the waters in order to be able to navigate them in the event of hostilities," Wiktorin is quoted as saying. "They could also be installing equipment, like sensors, that could track or get an observation of our units in that area," he goes on. "Or they could also possibly reconnoiter our (defense) systems." Russian military around the world . Whether there is a Russian sub in Swedish waters or not, there is no question that Russian forces have been active in the Baltic and around the globe this year. In fact, the Swedish military said Sunday that it has monitored suspicious activity for several years, according to another report in The Local. In July, a U.S. Air Force reconnaissance plane fled into Swedish airspace after the Russians took the unusual action of beginning to track it with land-based radar. The Russians then sent at least one fighter jet into the sky to intercept the U.S. aircraft. And on April 23, a Russian Su-27 Flanker fighter jet buzzed within 100 feet of the nose of a U.S. Air Force RC-135U reconnaissance plane over the Sea of Okhotsk between Russia and Japan, a Defense Department official said. Also on April 23, Dutch fighter jets scrambled to intercept a pair of Russian Tu-95 Bear bombers that entered a half-mile into Netherlands airspace. On June 4, according to U.S. defense officials, four long-range Russian Tu-95 bombers, accompanied by an aerial refueling tanker, flew into the U.S. Air Defense Identification Zone, an area extending 200 miles (320 kilometers) from the North American coast, off Alaska, where they were intercepted by U.S. F-22 fighter jets. Two of the Russian bombers peeled off and headed west, while the other two flew south and were identified by U.S. F-15 fighters within 50 miles of the California coast. And last month, two Alaskan-based U.S. Air Force F-22 fighter jets intercepted two Russian IL-78 refueling tankers, two Russian MiG-31 fighter jets and two Russian Bear long-range bombers, according to Capt. Jeff Davis of the North American Aerospace Defense Command. More than six hours later, two Canadian CF-18 fighter jets intercepted two Russian bombers in the Beaufort Sea, Davis said. Those Russian planes came within about 40 nautical miles of the Canadian coastline, he said. Earlier this year, a top U.S. Air Force general said Russia was stepping up its military activities in the Asia-Pacific region as tensions increased over Ukraine and Russia's move into Crimea.
Thursday after Swedish intelligence picked up an emergency radio call in Russian, reported The sent to the Russian enclave of Kaliningrad, 330 Russia on Sunday denied it has any vessel in question that Russian forces have been active in the Baltic and around the globe this year. In fact, the Swedish military said Sunday that it