( CNN ) -- Sweden wo n't exactly confirm that it 's been looking for a foreign submarine in the country 's territorial waters . But if it finds something it does n't like , it is ready to do whatever is needed to force it to the surface , a Swedish military spokeswoman said Tuesday . Swedish media have reported that the military has been looking for a mystery underwater vessel , possibly Russian . The search began Thursday after Swedish intelligence picked up an emergency radio call in Russian , reported The Local , citing the Swedish newspaper Svenska Dagbladet . `` We do n't know what it is , '' but we `` are prepared to use anything necessary to bring the vessel to the surface if we need to , '' Swedish military spokeswoman Therese Fagerstedt told CNN on Tuesday . Helicopters , battleships and minesweepers searched waters off Sweden 's capital , Stockholmm on Tuesday , The Local reported . Thursday 's 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 . U.S. officials told CNN there are no U.S. submarines or surface ships in the immediate area . U.S. intelligence does n't know of any Russian assets in that area , the officials said . Why would a Russian sub snoop around in Swedish waters ? 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 , '' `` Or they could also possibly reconnoiter our ( defense ) systems . '' CNN 's Ralph Ellis contributed to this report .
Navy , battleships and minesweepers hunt for vessel . Emergency radio call picked up by Swedish military , report says . Radio transmissions sent to Russian Navy on Baltic Sea , report says . Russia denies any vessel in Swedish waters .