Western officials have long been concerned about Moscow’s so-called shadow fleet, an assemblage of aged tankers created to covertly carry Russian crude oil around the world. Since Russia invaded Ukraine, the worry primarily concerned the use of such off-the-books ships to circumvent Western sanctions and generate revenue to fuel the Kremlin’s war machine.

But Russia’s shadow fleet may now present a more pressing danger to the West.

This week, Finnish commandos boarded an oil tanker that officials suspect had cut through vital underwater cables in the Baltic Sea, including one that carries electricity between Finland and Estonia. The ship, the Eagle S, bears all the hallmarks of vessels belonging to Russia’s shadow fleet, officials said, and had embarked from a Russian port shortly before the cables were cut.

“We know about Russia’s shadow fleet operating in our area, and we know Russia is systematically conducting hybrid warfare against its neighboring NATO/EU countries,” Lauri Läänemets, Estonia’s interior minister, said in an email to The New York Times. “It’s time to drop the illusions and face it.”