Investigators said they found a track on the seabed dozens of kilometres in length but have yet to find the anchor.
They have also questioned the crew of the Eagle S, which Finnish customs suspect to be part of a “shadow fleet” of ships transporting Russian crude and oil products, which are embargoed due to Russia’s invasion of Ukraine.
Elina Katajamaki of Finland’s National Bureau of Investigation said in the police statement the travel ban was a measure to ensure suspects can be contacted and the investigation is not compromised.
The number of suspects may change as the investigation continues, she added.
Nato’s secretary general, Mark Rutte, said the US-led defence alliance would bolster its military presence in the Baltic Sea in response to the incident.
A number of similar incidents targeting energy and telecommunications infrastructure have taken place in Baltic Sea since Russia’s invasion of Ukraine in February 2022, in what analysts suspect are part of “hybrid warfare” under way between Moscow and Western Europe.