Helsinki. Finnish investigators probing the damage to a Baltic Sea power cable and several data cables said they found an anchor drag mark on the seabed, apparently from a Russia-linked vessel that has already been seized.

The discovery heightened concerns about suspected sabotage by Russia's “shadow fleet” of fuel tankers — aging vessels with obscure ownership acquired to evade Western sanctions amid the war in Ukraine and operating without Western-regulated insurance.

The Estlink-2 power cable, which transmits energy from Finland to Estonia across the Baltic Sea, went down on Dec. 25 after a rupture. It had little impact on services but followed damage to two data cables and the Nord Stream gas pipelines, both of which have been termed sabotage.

Finnish police chief investigator, Sami Paila, said late Sunday the anchor drag trail continued for “dozens of kilometers ... if not almost 100 kilometers (62 miles).”

Paila added to Finnish national TV broadcaster Yle: “Our current understanding is that the drag mark in question is that of the anchor of the (seized) Eagle S vessel. We have been able to clarify this matter through underwater research."

Without giving further details, Paila said authorities have “a preliminary understanding of what happened at sea, how the anchor mark was created there,” and stressed that the “question of intent is a completely essential issue to be clarified in the preliminary investigation."

On Saturday, the seized vessel was escorted to anchorage in the vicinity of the port of Porvoo to facilitate the investigation, officials said. It is being probed under criminal charges of aggravated interference with telecommunications, aggravated vandalism and aggravated regulatory offense.

The Eagle S is flagged in the Cook Islands but was described by Finnish customs officials and the European Union executive commission as part of Russia’s shadow fleet of fuel tankers. Russia’s use of the vessels has raised environmental concerns about accidents given their age and uncertain insurance coverage.

In the wake of the cable rupture, NATO Secretary-General Mark Rutte said last week that the military alliance, which Finland joined last year, will step up patrols in the Baltic Sea region.

The Finnish Coast Guard said Monday that another tanker ship headed for a Russian port has engine failure and drifted, then anchored in the Gulf of Finland south of the Hanko Paninsula. The guard said it was notified Sunday night.

Registered in Panama, the M/T Jazz was en route to Primorsk, Russia, from Sudan, with apparently no oil cargo. Finnish authorities have dispatched a tugboat and a patrol ship to ensure that the vessel does not drift and to prevent any damage to the environment.

Regional director of the Coast Guard, Janne Ryönänkoski, said there was no immediate risk to the seabed infrastructure.

Earlier Monday, EU foreign policy chief Kaja Kallas said that “sabotage in Europe has increased" since Russia's full-scale invasion of Ukraine in February 2022.

Kallas told the German newspaper Welt that the recent “sabotage attempts in the Baltic Sea are not isolated incidents" but "part of a pattern of deliberate and coordinated actions to damage our digital and energy infrastructure.”

She vowed that the EU would “take stronger measures to counter the risks posed" by vessels of Russia's shadow fleet.

Finland, which shares a 1,340-kilometer (832-mile) border with Russia, abandoned its decades-long policy of neutrality and joined NATO in 2023, amid Russia's war against Ukraine.