Finland’s military has fired warning shots at a suspected ‘foreign submarine’ spotted in waters near Helsinki on Tuesday morning.

The navy fired handheld underwater depth charges as a warning message, Carl Haglund, Finland's defence minister, was quoted as saying by Reuters.

He said the target, which was spotted on Monday and then again in the early hours of Tuesday, could have been a submarine but did not comment on whether Russia was involved.

"We strongly suspect that there has been underwater activity that does not belong there. Of course it is always serious if our territorial waters have been violated," Mr Haglund told Finnish news agency STT.

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Commodore Olavi Jantunen told Helsingin Sanomat newspaper the bombs were to let the vessel know it had been noticed, not to cause it any damage.

Finland shares a 833 mile (1,340 km) border with Russia and has watched air force sorties and military border drills across Europe with growing concern.

In November, the European Leadership Network examined 39 incidents involving military encounters between Russia and Nato forces and allies over an eight-month period.