Britain's Royal Navy shadowed a Russian warship through the North Sea near United Kingdom waters on Christmas Day, the Royal Navy said Tuesday. It cited a recent "upsurge in Russian units transiting U.K. waters."

The Navy did not say why more Russian ships are traveling near or through U.K. waters. The activity comes amid soured relations between Britain and Russia over Moscow's annexation of Ukraine's Crimea, Russia's support for the regime of Syrian President Bashar Assad and allegations of Russian meddling in Britain's vote to leave the European Union — Brexit.

The Russian Admiral Gorshkov frigate was tracked by the HMS St. Albans, a Royal Navy frigate with 190 sailors on board. The Russian ship was also shadowed by a navy helicopter as it moved through what British officials called "areas of national interest."

Britain's Defense Secretary Gavin William said his country would not "hesitate in defending our waters or tolerate any form of aggression."

William added: "Britain will never be intimidated when it comes to protecting our country, our people and our national interests."

British officials previously warned that Russian ships transiting through U.K. waters risk cutting undersea Internet cables. These cables sit on the seabed and are a vital communication connection that link the country to continental Europe.