The Finnish authorities seized an oil tanker on Thursday on the suspicion that it was involved in cutting vital undersea cables and said the ship might have been part of Russia’s “shadow fleet,” aimed at evading Western sanctions.

In a statement, the police in Finland said the authorities had boarded the Eagle S tanker in Finnish waters. The ship, which is registered in the Cook Islands in the South Pacific, had been sailing from St. Petersburg, Russia, to Port Said, Egypt, when it was detained.

The police said they were investigating whether the vessel was involved in the latest suspected act of sabotage on undersea infrastructure: the cutting on Wednesday of the Estlink 2 submarine cable, which carries electricity between Finland and Estonia. The Finnish authorities said on Thursday that four other cables carrying data also had been damaged. The police called the latest cable cuts “aggravated vandalism”.

The Finnish authorities said the tanker might be part of Russia’s shadow fleet, which emerged as a way to circumvent Western-imposed price caps on Russian oil transported by sea. The caps were introduced several months after President Vladimir V. Putin of Russia ordered the full-scale invasion of Ukraine in February 2022.

To skirt the restrictions, the Kremlin invested billions of dollars in a fleet of mostly unmarked tankers not easily traced to Russia. Many sail under the flags of other nations, like the Central African country of Gabon, and sell to buyers in countries like India and China, which are not bound by the price cap.

The goal was largely economic and mostly successful. Since the oil price cap was enacted, nearly 70 per cent of Russia’s oil is being transported by so-called shadow tankers, according to an analysis published in October by the Kyiv School of Economics Institute, a Ukraine-based think tank.

But the use of such tankers to intentionally sabotage European infrastructure would be an unusual escalation.

“We assume at this stage that the vessel in question is a member of the shadow fleet,” the head of Finland’s customs agency, Sami Rakshit, told a news conference, without providing further details.

Finland’s Prime Minister, Petteri Orpo, said that while there was no direct evidence linking the Eagle S to Russia, the incident underscored the Baltic nations’ vulnerability to potential meddling by Moscow.

“This underlies the danger of the shadow fleet in the Baltic Sea,” Orpo said at a news conference in Finland’s capital, Helsinki.

“Our main task is to find effective means to stop the shadow fleet,” Orpo added. “The shadow fleet pumps money into Russia’s war fund so that Russia can continue to wage its war in Ukraine against the people of Ukraine, and it has to be stopped.”

He said the Finnish government had not been in touch with Russia. After its seizure, the Eagle S was anchored in Finnish waters, as the Finnish authorities investigated, working with the Estonian authorities.

The investigation comes as a number of other undersea cables have been cut in recent months, raising fears of a covert campaign against Nato nations that have supported Ukraine in the face of Moscow’s full-scale invasion.

Mark Rutte, the Nato secretary-general, said on Thursday that he had spoken to Estonia’s Prime Minister, Kristen Michal, about the “possible sabotage” of the undersea cables.

Nato “stands in solidarity with allies and condemns any attacks on critical infrastructure,” Rutte wrote on social media, adding, “We stand ready to provide further support”.

After a series of undersea explosions blew apart the Nord Stream natural gas pipelines linking Russia to Western Europe in the fall of 2022, Western intelligence agencies said the evidence pointed towards pro-Ukraine forces, even if the question of who might have been directing them remained a mystery.

Last month, two fibre-optic cables were cut in the Baltic Sea in what Germany’s defence minister described as an act of sabotage. One cable connected Finland and Germany; the other ran between Lithuania and Sweden — all countries that are members of the Nato alliance.

Russian ships have been reported in the Baltic and North Seas near areas where critical infrastructure lies beneath the water, and dozens of Russian tankers have begun sailing under different flags.

New York Times News Service