The Finnish military says it has dropped depth charges onto a suspected submarine in the sea outside Helsinki after twice detecting the presence of a foreign object . The navy said it noticed an underwater target yesterday and again this morning and fired some warning charges the size of grenades . Finland , which shares an 833-mile border with Russia , has been increasingly worried about its powerful neighbour after a year of Russian air force sorties and military border exercises . A Finnish coastguard ship tracks the underwater object - believed to have been a Russian submarine - in the waters near the capital Helsinki . Border patrol boats first identified an underwater target yesterday , before detecting it again early this morning and dropping 'warning ' depth charges . Finland defence minister Carl Haglund did not say whether Russia was involved but told local media that it was extremely rare for the military to use such warning charges . Pictured is a Finnish navy boat . The Finland incident comes just months after Sweden 's armed forces hunted unsuccessfully for what they believed to have been a foreign submarine close to Stockholm . It comes just months after Sweden suspected Russia of sending a vessel into waters close to the capital Stockholm . In what was Sweden 's biggest mobilisation since the Cold War , its navy hunted unsuccessfully for a week for what they believed to be a foreign submarine after several observations were made . Swedish officials never blamed any country , though most defense analysts said Russia was a likely culprit . Today Finland defence minister Carl Haglund did not say whether Russia was involved but told local media that the target could have been a submarine , and that it has likely left the area , adding that Finland has rarely used such warning charges . He said : 'We strongly suspect that there has been underwater activity that does not belong there . Finland first alerted its navy to a 'possible underwater target ' about midday yesterday . 'Of course it is always serious if our territorial waters have been violated , ' he told Finnish news agency STT . Moscow retorted immediately , saying moves by Finland and Sweden towards closer ties with NATO were of 'special concern ' . In a statement , the Finland Ministry of Defence said its surveillance system first alerted its navy to a 'possible underwater target ' within territorial waters about midday yesterday . A second detection was then made early this morning after the navy began searching for the object , and underwater depth charges were fired at 3am . Commodore Olavi Jantunen told Helsingin Sanomat newspaper : 'The bombs are not intended to damage the target , the purpose is to let the target know that it has been noticed . ' Reports of a submarine spotted off Stockholm last year led to Sweden 's biggest mobilization since the Cold War . Regional tensions were reflected earlier in April after an unprecedented hawkish joint statement by Nordic countries - Sweden , Norway , Finland , Denmark and Iceland - that directly cited the Russian 'challenge ' as grounds to increase defense cooperation .
The Finnish military has dropped depth charges on a possible submarine . Its navy twice detected a foreign object within Helsinki territorial waters . The charges released were warning shots , about the size of hand grenades . Comment: