The owner of an oil tanker seized by Finland on suspicion of breaking an undersea power line and four telecoms cables in the Baltic Sea last week is seeking the release of the ship, a lawyer representing the company said on Monday.

Finnish police and coast guard officials boarded the Cook Islands-registered Eagle S on Thursday and brought it to a location near a Finnish port where crew members are being questioned.

Finland's president last week said he believed further damage would have occurred on the seabed had the ship not been stopped.

Finland's customs service has said it believes the Eagle S is part of a shadow fleet of ageing tankers being used to evade sanctions on the sale of Russian oil, and has formally impounded its cargo although it is still on board the ship.

The owner of the Eagle S, United Arab Emirates-based Caravella LLC FZ, filed a request with the Helsinki District Court on Monday to cancel the seizure of the ship.

Finnish lawyer Herman Ljungberg, who filed the documents on behalf of the company, said authorities had not provided any explanation of the legal basis for taking the vessel into custody and boarding it.

"The Finns have hijacked a vessel," Ljungberg told Reuters.

He said the crew had been interrogated by investigators without any legal assistance and that they had been deprived of sleep.

A police spokesperson said the seizure of the vessel had taken place according to Finnish law and that crew members had been informed of their rights, including that of legal assistance.

They had not been deprived of sleep, the spokesperson added.