London, Dec 26 (IANS): A British frigate has escorted a Russian warship through the North Sea near UK waters on Christmas Day, the Royal Navy has revealed. Russia has not commented on the issue, the BBC reported.

In a statement, the Royal Navy said HMS St Albans was called upon to sail on December 23, and "keep watch on new Russian warship Admiral Gorshkov as it passed close to UK territorial waters".

It said the British frigate remained at sea on Christmas Day, monitoring the Russian vessel. It would return to Portsmouth on Boxing Day.

The Royal Navy said HMS St Albans monitored the Admiral Gorshkov's "activity in areas of national interest". It said there has been an "upsurge in Russian units transiting UK waters".

Britain has also earlier warned of a new threat posed by Russia to internet cables under the sea, the BBC said.

Air Chief Marshal Sir Stuart Peach, the chief of the defence staff, said earlier in December, Britain and Nato needed to prioritise 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.

"I will not hesitate in defending our waters or tolerate any form of aggression," Defence Secretary Gavin Williamson said. "Britain will never be intimidated when it comes to protecting our country, our people, and our national interests."

The Royal Navy said that HMS Tyne was also called to escort a Russian intelligence-gathering ship through the North Sea and the English Channel on Christmas Eve.

Meanwhile, a navy helicopter was scrambled to track two other Russian vessels, the BBC said.

In January 2017, a British warship and three RAF Typhoons escorted a Russian aircraft carrier and a number of other ships up the English Channel.

Relations between Britain and Russia have remained tense since Moscow's annexation of Ukraine's southern Crimea peninsula in 2014.