LONDON — Ruptures of undersea cables that have rattled European security officials in recent months were likely the result of maritime accidents rather than Russian sabotage, according to several U.S. and European intelligence officials.

The determination reflects an emerging consensus among U.S. and European security services, according to senior officials from three countries involved in ongoing investigations of a string of incidents in which critical seabed energy and communications lines have been severed.

The cases raised suspicion that Russia was targeting undersea infrastructure as part of a broader campaign of hybrid attacks across Europe, and prompted stepped-up security measures including an announcement last week that NATO would launch new patrol and surveillance operations in the Baltic Sea.

But so far, officials said, investigations involving the United States and a half-dozen European security services have turned up no indication that commercial ships suspected of dragging anchors across seabed systems did so intentionally or at the direction of Moscow.

Instead, U.S. and European officials said that the evidence gathered to date — including intercepted communications and other classified intelligence — points to accidents caused by inexperienced crews serving aboard poorly maintained vessels.

U.S. officials cited “clear explanations” that have come to light in each case indicating a likelihood that the damage was accidental, and a lack of evidence suggesting Russian culpability. Officials with two European intelligence services said that they concurred with U.S. assessments.

Despite initial suspicions that Russia was involved, one European official said there is “counter evidence” suggesting otherwise. The U.S. and European officials declined to elaborate and spoke on the condition of anonymity, citing the sensitivity of ongoing investigations.

The probes center on three incidents over the past 18 months in which ships traveling to or from Russian ports were suspected of severing key links in a vast underwater network of conduits that carry gas, electricity and internet traffic to millions of people across northern Europe.

In the most recent case, Finland seized an oil tanker suspected of dragging its anchor across an undersea power line connecting Finland and Estonia. Finnish authorities said the vessel, the Eagle S, is part of a “shadow fleet” of tanker ships helping Moscow sell oil on global markets in violation of international sanctions.

Previous cases involved a Hong Kong-registered container ship, the NewnewPolar Bear, that ruptured a natural gas pipeline in the Gulf of Finland in October 2023, and a Chinese ship, the Yi Peng 3, that cut two data cables in Swedish waters in November last year.

Russia’s denials of responsibility have been greeted with deep skepticism by European officials confronting a broader wave of hybrid attacks attributed to Moscow.

U.S. and European security officials last year disrupted an alleged Russian plot to smuggle incendiary devices on cargo planes in an apparent trial run for later attacks targeting the United States and Canada. U.S. intelligence officials also warned German authorities that Russia was planning to assassinate the chief executive of one of Europe’s largest weapons producers, a company that had announced plans to build an ammunition manufacturing facility in Ukraine.

At the same time, European security officials have accused Russia of using proxies to carry out hundreds of arson attacks, rail disruptions and smaller sabotage operations aimed at sowing divisions in Europe and sapping support for Ukraine.

Against that backdrop, the damage to seabed systems added to a European sense of being under siege. German Defense Minister Boris Pistorius called the anchor-dragging incident in November “sabotage” and said “nobody believes that these cables were accidentally severed.” Weeks later, Finnish President Alexander Stubb said a Christmas Day incident was “definitely” linked to Russia.

Experts have also said that the seabed cases fit a pattern of Russian aggression.

The severing of cables “may very well be random accidents,” said Eric Ciaramella, a senior fellow at the Carnegie Endowment for International Peace who previously served as the United States’ deputy national intelligence officer for Russia. “But it’s hard to rule out a concerted Russian campaign when [Moscow’s] intelligence services are trying to assassinate German business executives, starting fires at factories across Europe, and putting bombs on cargo planes.”

The emerging view among Western spy agencies that accidents — and not Russia — are likely to blame for the undersea damage was dismissed by some critics of Russia.

Pekka Toveri, who represents Finland in the European Parliament and previously served as the country’s top military intelligence official, said that the seabed cases are part of “a typical hybrid operation” from Moscow.

“The most important thing in any hybrid operation is deniability,” Toveri said. Russia’s security services may have succeeded in not leaving “any proof that would hold up in court,” he said, but to conclude that they were accidents “is total B.S.”

Toveri and others cited anomalies in the behavior of the vessels involved as well as evidence that Russia has for decades devoted extensive resources — including a dedicated military unit known as the General Staff Main Directorate for Deep Sea Research — to mapping Western seabed infrastructure and identifying its vulnerabilities.

At least two of the ships suspected of causing damage appear to have dragged their anchors 100 miles or more across seafloor. A ship that dropped an anchor by accident, Toveri said, would immediately be dragged so noticeably off course that crews would scramble to bring the vessel to a stop and assess the damage.

Mike Plunkett, naval expert at Janes, said that “aside from a very loud splash, there will also be a lot of noise from the anchor chain paying out through the hawse hole.” He described the chances of three anchor-dropping incidents in the Baltic region since 2023 as “vanishingly small” although not zero. But he said it was extremely difficult to prove intentional sabotage.

The timing of the incidents has heightened suspicion. The most recent cases, in November and December, damaged undersea energy lines at a time when Baltic nations are accelerating efforts to disconnect their power grids from Russia — a move that gained urgency after Russia’s 2022 invasion of Ukraine.

There are also reasons to question why Russia would risk targeting undersea systems in waterways now lined by NATO-member countries. Doing so could endanger oil smuggling operations Russia has relied on to finance the war in Ukraine, and possibly provoke more aggressive efforts by Western governments to choke off Russia’s route to the North Atlantic.

At a Baltic summit in Helsinki on Jan. 14, NATO Secretary General Mark Rutte announced plans for new patrols by frigates, aircraft, submarine satellites and a “small fleet of naval drones” designed to detect undersea sabotage.

Despite advances in undersea surveillance capabilities, attributing attacks has proved difficult. The bombing of the Nord Stream gas pipelines between Russia and Germany in September 2022 was initially widely blamed on Russia but is now believed to have been carried out by a senior Ukrainian military officer with deep ties to the country’s intelligence services.

Finland took a more aggressive approach to the Dec. 25 case of cable damage, forcing the Eagle S into Finnish waters before police and coast guard authorities boarded the vessel by helicopter. Members of the crew suspected of being on duty during the anchor-dragging damage are barred from leaving Finland while the investigation moves forward.

A Nordic official briefed on the investigation said conditions on the tanker were abysmal. “We’ve always gone out with the assumption that shadow fleet vessels are in bad shape,” the official said. “But this was even worse than we thought.”

Herman Ljungberg, a lawyer who represents the owner of the Eagle S tanker, acknowledged in a telephone interview that the vessel was carrying Russian oil but denied that it was in violation of international law or that the crew had intentionally caused any damage.

European security officials said that Finland’s main intelligence service is in agreement with Western counterparts that the Dec. 25 incident appears to have been an accident, though they cautioned that it may be impossible to rule out a Russian role.

A spokeswoman for Finland’s National Bureau of Investigation, which is leading the investigation of the Eagle S, said that the bureau’s probe is “still open, and it is too early to make final conclusions of the causes or combinations behind the damages.”

Dixon reported from Riga, Latvia, and Stanley-Becker from Washington. Ellen Francis in Brussels contributed to this report.

previous coverage

• Estonia steps up patrols in the icy Baltic Sea in a show of force after suspected cable sabotage

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