The United Kingdom's Royal Navy says it has escorted a Russian warship through the North Sea near British territorial waters.
The Royal Navy said in a December 26 statement that the frigate HMS St Albans departed on December 23 to monitor the Russian warship Admiral Gorshkov as it moved through the North Sea.
The Royal Navy said its vessel monitored the Russian ship over December 25 and will return to dock in Britain on December 26.
Russia has yet to comment.
The Royal Navy said there had been a recent "upsurge in Russian units transiting U.K. waters."
U.K. Defense Secretary Gavin Williamson said in a statement after the incident that he would "not hesitate in defending our waters or tolerate any form of aggression."
"Britain will never be intimidated when it comes to protecting our country, our people, and our national interests," he added.
The Royal Navy said another British frigate was called to escort a Russian intelligence-gathering ship through the North Sea and the English Channel on December 24.
Meanwhile, a navy helicopter was sent to monitor two other Russian vessels.
Britain's military chief, Sir Stuart Peach, said earlier this month that Russia could pose a major threat to NATO countries by attacking underwater communication cables crucial for international trade and the Internet.
He said it would "immediately and potentially catastrophically" hit the economy if they were cut or disrupted.
Bilateral relations between Britain and Russia have been severely strained by differences over Ukraine and Syria as well as by allegations of Russian meddling in domestic politics in Europe and the United States.
Russia denies the accusations.
The 2006 radiation-poisoning death in London of Aleksandr Litvinenko, a former officer with Russia's Federal Security Service (FSB) has also continued to cast a shadow over ties between the two countries.