The UK warned Vladimir Putin against damaging Britain’s undersea cables and pipelines after a month-long operation to track three Russian submarines in nearby waters.

Some 500 military personnel were involved in the surveillance effort, with Royal Navy vessels covering thousands of miles and Royal Air Force planes flying for more than 450 hours, Defense Secretary John Healey told reporters. A Russian Akula-class submarine and two specialist submarines with GUGI, Russia’s deep-sea research directorate, have now left UK waters, he said.

“To President Putin, I say, ‘We see you,’” Healey said on Thursday. “‘We see your activity over our cables and our pipelines. And you should know that any attempt to damage them will not be tolerated and will have serious consequences.’”

The presence in and around UK waters of the Russian submarines highlights the growing threat posed by Russia to cables and other offshore infrastructure in what Healey has previously described as a “reckless campaign of sabotage across Europe.” NATO last year stepped up patrols in the Baltic Sea following suspected sabotage of undersea cables between Finland and Estonia.

On Thursday, the defense secretary said there was no evidence the recent Russian operation had caused any damage to Britain’s pipes and cables, but that the UK would work to verify that assessment.

The episode unfolded at a time when global attention was largely focused thousands of miles away in the Middle East. The UK has in recent weeks led international calls to disrupt the “shadow fleet” of tankers transporting Russian oil, with Prime Minister Keir Starmer last month announcing that the UK would board vessels suspected to part of the fleet that transit British waters.

Healey said the activity highlights why the seabed matters, pointing out that as an island nation, Britain gets half the gas that heats households as well as 99% of international telecoms and data traffic through seabed infrastructure.

“Connection is everything for our economy and for our security, and beneath our waters lies a vast network of cables and pipelines on which our way of life depends,” Healey said. “The UK’s undersea network is highly resilient, but the threats are increasing, and so we’re stepping up our action to defend it.”

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