Finnish police and border guards boarded the vessel, the Eagle S, just past midnight on Thursday and took over the command bridge, Helsinki Police Chief Jari Liukku said at a news conference.
The vessel was intercepted in Finland's exclusive economic zone and taken to Finnish territorial waters, police said.
The Eagle S is flagged in the Cook Islands but was described by Finnish customs officials as a suspected part of Russia's shadow fleet of fuel tankers, Yle television reported.
Those are aging vessels with obscure ownership, acquired to evade Western sanctions over the war against Ukraine and operating without Western-regulated insurance.
The Eagle S's anchor is suspected of causing damage to the cable, Yle reported, relying on police statements.
The Estlink-2 power cable, which brings electricity from Finland to Estonia across the Baltic Sea, went down just after noon on Wednesday.
The incident follows damage to two data cables and the Nord Stream gas pipelines, both of which have been termed sabotage.
The Estonian government met in an emergency session over the incident.
The shadow tankers "are helping Russia to earn funds that will aid Russian hybrid attacks," Prime Minister Kristen Michal said at a news conference.
"We need to improve the monitoring and protection of critical infrastructure both on land and on sea."
He said repairs to the cable could take as long as seven months.
"Repeated damage to Baltic Sea infrastructure signals a systemic threat, not mere accidents," Estonia's President Alar Karis said on X.
"Estonia will take action to counter this threat, together with Finland and other NATO allies."
Repeated damage to Baltic Sea infrastructure signals a systemic threat, not mere accidents. — Alar Karis (@AlarKaris) #Estonia will take action to counter this threat, together with #Finland and other #NATO allies.December 26, 2024
Two data cables — one running between Finland and Germany and the other between Lithuania and Sweden — were severed in November.
Germany's defence minister said officials had to assume the incident was "sabotage," but he did not provide evidence or say who might have been responsible.
The remark came during a speech in which he discussed hybrid warfare threats from Russia.
The Nord Stream pipelines that once brought natural gas from Russia to Germany were damaged by underwater explosions in September 2022.
Authorities have said the cause was sabotage and launched criminal probes.
Estonian network operator Elering says there was enough spare capacity to meet power needs on the Estonian side, public broadcaster ERR said.
