Britain warned on Wednesday that it faced a growing threat of aggression from Russia, claiming that a Russian spy ship had passed the English coast for the second time in three months, in the latest incident that appeared to be designed to test Britain’s military capabilities.

John Healey, Britain’s defense secretary, told parliament that two Royal Navy ships had been deployed for two days to monitor the passage of the Yantar, which he described as a Russian spy ship used to gather intelligence and map critical British underwater infrastructure.

The incident is the latest in a series of incursions by Russian ships and aircraft around Britain, and comes amid growing concern in Europe about threats to critical infrastructure and possible sabotage, with Western intelligence warning of the Kremlin’s intention to punish Europe for its support for Ukraine. Last year, when the Yantar was first discovered in British waters, a British submarine was tracking it nearby, the Defense Secretary revealed on Wednesday.

While authorities have linked Russian intelligence to vandalism, arson and attacks across Europe in recent years, threats at sea have caused the most concern and prompted the boldest responses. Last week, NATO announced it was deploying warships, patrol planes and drones to protect critical infrastructure in the Baltic Sea after several underwater cables were cut, apparently by ships dragging their anchors on the seabed.

Suspicion fell on ships connected to Russia and China, with European Union ships surrounding the ship under the Chinese flag for weeks and Finland seizure of the oil tanker which experts and officials said could be part of Russia’s efforts to avoid Western sanctions.

Russian Navy vessels have been carrying out missions near Britain and elsewhere for years. But Mr. On Wednesday, Healey provided an unusual amount of detail about the otherwise murky world of military surveillance, highlighting growing concerns about Russian activity, particularly over vital undersea cables linking Britain to mainland Europe.

“Russia remains the most pressing and immediate threat to Britain,” said Mr. Healey on Wednesday, adding that he wanted to send a message to Russian President Vladimir V. Putin. “We see you. We know what you’re doing. And we will not shy away from strong actions to protect this country,’ he said.

Mr Healey also told MPs he had changed the naval rules of engagement to allow two British ships to approach and track the movements of the Yantar, which has since gone into Dutch waters.

Last November, the Yantar was spotted hovering over critical British undersea infrastructure, Mr. Healey, adding that on that occasion he authorized a Royal Navy submarine to surface near Yantar to demonstrate that it was under surveillance.

At the time, the British said, the Yantar was escorted by the frigate Admiral Golovko and the accompanying tanker Vyazma, before the ships headed for the Mediterranean.

The Yantar, which has been in service for about a decade, is a highly sophisticated spy ship developed by Russia’s General Directorate for Deep Sea Exploration specifically to search for critical underwater cables, said Justin Crump, CEO of the private intelligence firm Sibylline, which has monitored the ship for years. . The ship is equipped with two autonomous submarines that can operate extensively and largely undetected, he said.

Although Yantar might be capable of sabotage, said Mr. Crump, it is more likely that the ship will be used to find and possibly tap cables to gather intelligence, and perhaps map their locations for future operations.

“They have invested a lot of time and money in the development of these ships, which have many impressive capabilities in this area,” he said. “And actually, to break a pipeline or a cable, they realized they could just drag the anchor to the seabed.”

Although intelligence agencies and experts say the cutting of underwater cables fits into what is believed to be a secret Kremlin plan, it has proven difficult to actually uncover evidence linking Russia to the recent episodes. The Kremlin has denied involvement in the sabotage.

On Wednesday, Finnish authorities announced that a preliminary investigation into the cutting of several critical underwater cables last month was nearing completion, but said it was too early to say whether any country was behind it. Investigators have concluded that the seized oil tanker, the Eagle S, which sailed from a Russian port shortly before the cables were cut, dragged its anchor up to 100 kilometers on the seabed, a process that experts say could hardly have been accidental. .

Shipping experts have identified the Eagle S as a member of Russia’s so-called shadow fleet, a group of old tankers used by Moscow to secretly transport crude around the world to fuel its war machine in Ukraine. The tanker and its crew remain in Finnish custody.

Russia has long shown interest in the Western undersea cable network, experts say. Over the past few years, Russian naval and merchant ships have spent time off the coast of Ireland, where bundles of underwater cables connect Europe and North America.

“What we don’t know is why they’re doing it,” said Elisabeth Braw, a senior fellow at the Atlantic Council who researches Russian naval activities.

“Are they just signaling that we can sit on top of the underwater cables as long as we want and you can’t do anything?” she asked. “Are they conducting reconnaissance of future actions that they might take and are they conducting some kind of adversary activity?

Countries can do little about it, Ms. Braw said, because international maritime law does not prevent Russian ships from operating in those areas.

Alistair Carmichael, the British MP representing the Orkney and Shetland Islands, said “Yantar’s activities could be an escalation”. But he added that for almost two years he had been warning about Russian ships operating around the Shetland Islands, north of mainland Scotland.

“This is a strategic threat to the UK as a whole, but it is particularly acute for our island communities who rely on cables for digital and energy connectivity,” he told parliament.

Britain has been one of Ukraine’s most vocal supporters since Russia invaded it in 2022, and tensions between London and Moscow rose last year when Ukraine fired British Storm Shadow missiles in the Russian Kursk region.

Amid rising tensions last October, Ken McCallum, head of MI5, Britain’s internal security service, said they were Russian intelligence agents were on a mission to “wreak havoc on British and European streets”. He accused Russia’s military intelligence agency of “dangerous actions carried out with increasing recklessness,” including cases of “arson, sabotage, and more.”

In April, British prosecutors charged five men with working on behalf of Russia to set fires at a Ukraine-linked company in Britain. And last fall, officials said fires at shipping facilities in Britain and Germany were caused by incendiary devices likely planted by Russian operatives.

Britain has recently reported more overt Russian military actions. In September last year, it was reported that British Typhoon jets had taken off to intercept two Russian Bear-F jets flying near British airspace. It also said the British navy had tracked four Russian vessels, including a Kilo-class submarine, through the English Channel and the North Sea.

Johann Lemola contributed reporting from Helsinki.