Several subsea telecom and power cables have been severed in the Baltic Sea in recent months in incidents that experts and politicians say are part of hybrid war actions orchestrated by Russia.

Leaders of NATO countries bordering the Baltic Sea are to meet in Helsinki on Tuesday to discuss security in the region, with NATO Secretary General Mark Rutte expected to attend.

The meeting will focus on the "strengthening of NATO's presence in the Baltic Sea and responding to the threat posed by Russia's shadow fleet," Finland's President Alexander Stubb said in a statement last week.

Finland has said NATO would contribute two vessels to the monitoring mission, while the British-led Joint Expeditionary Force (JEF), which comprises Nordic and Baltic states as well as the Netherlands, also said it would increase its surveillance.

"The (Swedish) government has commissioned the Swedish Armed Forces to contribute up to three warships and an air and sea surveillance plane, the ASC890," Prime Minister Ulf Kristersson told reporters on Sunday.

On December 25, the Estlink 2 electricity cable and four telecom cables linking Finland and Estonia were damaged, just weeks after two telecom cables in Swedish waters of the Baltic Sea were severed on November 17-18.

Suspicion over the Christmas Day incident has fallen on the Eagle S, a Cook Island-flagged oil tanker believed to be part of Russia's "shadow fleet".

The "shadow fleet" consists of ships that carry crude oil and petroleum products embargoed over Moscow's invasion of Ukraine.

The often ageing vessels operate under opaque ownership or without proper insurance.

Finnish police seized the Eagle S on December 28 as part of a criminal investigation into suspected sabotage.

The ship is anchored in Porvoo, east of Helsinki.

Finnish authorities last week deemed the ship unseaworthy following an inspection, barring it from sailing, and had previously banned eight crew members from leaving the country while police carry out a probe.

Investigators suspect the cables were damaged by the tanker's anchor being dragged over them.

Police earlier this week said that the anchor had been recovered from the seabed.