The British government said Thursday it had exposed what it described as a covert Russia submarine operation around pipelines and cables in waters north of the United Kingdom.

A Russian attack submarine and vessels from the country’s Main Directorate of Deep Sea Research (GUGI) were involved in what the UK Ministry of Defence called “nefarious activity over critical undersea infrastructure elsewhere.”

The MoD said GUGI operates specialized deep-sea units that survey underwater infrastructure during peacetime in preparation for sabotage during a conflict.

UK Defense Secretary John Healey said British ships, aircraft and allied forces tracked the three Russian submarines over several weeks and dropped sonobuoys to inform the submarine units they were being monitored and their mission was “no longer covert as Putin had planned.”

The Russian vessels “subsequently retreated home, having failed to complete their operation in secrecy,” said the MoD.

Officials did not report any damage to undersea infrastructure.

Healey said the Russian activity threatened both pipelines and cables but declined to specify where it took place. There are no pipelines north of the United Kingdom, with the most critical energy connections running through the North Sea on the country’s east coast to Norway.

The Defense Secretary stated: “To Putin, I say this: we see you, we see your activity over our underwater infrastructure. You should know that any attempt to damage it will not be tolerated and would have serious consequences.”

The British government said the activity formed part of a wider effort by Russia to operate in areas where critical seabed infrastructure is located. It said it disclosed the details to draw attention to the potential risks such activity poses to the UK’s connectivity.

“Undersea fibre-optic cables connect the UK to the world,” the Ministry of Defence said in a statement. “Over 99% of international data — from communications to trade — travels through subsea infrastructure. Protecting it is vital to the UK’s economic security, global connectivity and national resilience.”

John Hardie, the Russia program deputy director at the Foundation for Defense of Democracies, said: “GUGI, which has dedicated seabed warfare capabilities, has long engaged in suspicious activity near undersea cables. Russia can use these vessels to place wiretaps or collect intelligence to support contingency planning to disrupt NATO communications in the event of war.”

The UK is not only itself dependent on subsea cables for its own connectivity to the rest of the world but also a major hub for transatlantic data, with cables linking North America and Europe landing at a limited number of British coastal sites, making the country both strategically vital and potentially vulnerable.

Western officials have increasingly warned that such infrastructure could be targeted as part of so-called hybrid warfare, particularly since Russia’s full-scale invasion of Ukraine in 2022. A spate of data cable breaks in the Baltic Sea have provoked concerns about sabotage, although European officials are increasingly certain these have been accidental.

The latest developments highlight the intersection of physical and cyber security, as damage to undersea cables could disrupt financial systems, communications and essential services far beyond the immediate area of any incident.

British officials say they will continue to increase surveillance and cooperation with allies to safeguard undersea infrastructure, which they describe as a cornerstone of national security in an increasingly contested maritime environment.