On December 25, the EstLink 2 electricity cable and four telecom cables that lie on the seafloor linking Finland and Estonia went offline after suspected sabotage.

The incident occurred just weeks after other cables in the Baltic sea were severed in similar incidents that experts and politicians say are part of a hybrid war between Russia and Western countries.

Suspicion over the December 25 incident has fallen on the Eagle S, an oil tanker flying the Cook Islands flag and that's thought to be part of Russia's so-called "shadow fleet" -- ships that carry Russian crude oil and petroleum products, which are embargoed over Moscow's invasion of Ukraine.

Finnish police said on December 29 that they had found a drag trail stretching dozens of kilometres (miles) along the seabed.

Investigators suspect that the cables were damaged after the tanker's anchor was dragged over them.

Sweden last week sent a submarine rescue vessel to assist Finland in the investigation and on Tuesday said that the anchor had been recovered.

"The HMS Belos has located and lifted the anchor and handed it over to Finnish authorities," Swedish navy spokesman Jimmie Adamsson told AFP.

Finnish police said in a statement on Tuesday that the anchor had been retrieved in the afternoon on Monday.

Finland seized the tanker on December 28 and has banned eight crew members from leaving Finnish territory.

Finnish customs have said they suspect the tanker, currently located east of Helsinki, is part of Russia's so-called "shadow fleet".

Finnish telecom operator Elisa said Monday that two of the four damaged telecom cables had been repaired.

On Tuesday, a telecom cable running between Finland and Germany, which was damaged in a separate incident, had also been restored, operator Cinia said.

The Estlink 2 power cable has not yet been repaired.

In late December, NATO announced it would strengthen its military presence in the Baltic after similar incidents there since Russia's 2022 invasion.

The British-led Joint Expeditionary Force (JEF) announced Monday it would increase its surveillance of undersea infrastructure in the Baltic Sea in response to recent events.

Energy and communications infrastructure in particular have been targeted as part of what experts and politicians call Russia's "hybrid war" with Western countries.

The Baltic is surrounded by a number of NATO member states.

Two telecommunications cables were cut on November 17 and 18 in Swedish territorial waters.

A Chinese-flagged bulk carrier, the Yi Peng 3 is suspected of involvement.