The Royal Navy has been monitoring a Russian spy ship which entered British waters earlier this week, defence secretary John Healey told the Commons.
Healey said he wanted Putin to know "we see you, we know what you're doing and we will not shy away from robust action to protect this country".
It's the second time the Russian vessel, named Yantar, was used for intelligence gathering in British waters in recent months.
Report by Faragt.
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