A British naval frigate escorted a Russian warship through the North Sea near UK waters on Christmas Day, the Royal Navy confirmed.
The HMS St. Albans monitored the Russian vessel Admiral Gorshkov as it made its way across the North Sea close to Britain.
Although such crossings are fairly routine, there has been a rise in the number of Russian ships passing close to British territorial waters in recent days.
The Royal Navy said there had been a recent "upsurge in Russian units transiting UK waters". Britain recently warned of a new threat posed by Russia to internet cables under the sea.
Air Chief Marshal Sir Stuart Peach, the chief of the defense staff, said earlier this month that Britain and NATO needed to prioritize protecting the lines of communication.
He said it would "immediately and potentially catastrophically" hit the economy if they were cut or disrupted.
The cables criss-cross the seabed, connecting up countries and continents.