Finnish police have detained a vessel sailing from Russia, which is suspected of damaging an undersea telecoms cable running from Helsinki to Estonia across the Gulf of Finland.

The cargo vessel, the Fitburg, was sailing from St Petersburg to the port of Haifa in Israel, under the flag of St Vincent and Grenadines.

All 14 crew members were arrested after the cable owned by Finnish telecoms operator Elisa was damaged. The operator said in a statement that the damage had "not affected the functionality of Elisa's services in any way", and its services had been re-routed.

The Baltic Sea has seen a series of incidents in recent years in which underwater cables have been damaged or completely cut.

Many experts and political leaders have viewed the recent incidents as part of a "hybrid war" carried out by Russia against Western countries. The issue has come under increased focus since the Russian invasion of Ukraine in 2022.

Police said they were investigating "aggravated disruption of telecommunications" and "aggravated sabotage and attempted aggravated sabotage".

The detained crew members were Russian, Georgian, Kazakh and Azerbaijani, police added.

Undersea cables carry crucial electricity and data between countries, and keep people connected to the internet.

On Wednesday morning, the Finnish authorities sent a helicopter and a patrol ship to the area, where they found the vessel was dragging its anchor in the sea, Finland's coastguard said.

They said they had "launched operations this morning to investigate the suspected cable damage" after telecoms provider Elisa detected a fault.

Finnish police said the authorities had "taken control of the vessel as part of a joint operation".

"At this stage, the police are investigating the incident as aggravated criminal damage, attempted aggravated criminal damage, and aggravated interference with telecommunications," the police added.

"Finland is prepared for security challenges of various kinds, and we respond to them as necessary," Finnish President Alexander Stubb said in a statement on social media.

At a press conference, police were asked by journalists if the cable was damaged on behalf of another country, local media reported.

Police Chief Ilkka Koskimäki replied that "the police or other authorities do not speculate on these matters. The police's job is to investigate what happened."

Eight Nato countries, and Russia, border the Baltic Sea - Finland, Estonia, Denmark, Germany, Latvia, Lithuania, Poland and Sweden.

Estonia's government said a second telecoms cable connecting it to Finland also suffered an outage on Wednesday. The country's President Alar Karis said "hopefully it was not a deliberate act, but the investigation will clarify".

The European Commission was closely monitoring the incident, EU technology commissioner Henna Virkkunen posted on X, adding that it was prepared to counter "hybrid threats".

"We're already talking about national security. Critical infrastructure is the front line," the Finnish MP Jarno Limnell commented on the incident, in a post on X.

Nato has identified deep-sea cables as part of the world's critical infrastructure and previously warned that adversaries could exploit them through sabotage or hybrid warfare, threatening both civilian and military communications.

"Hybrid warfare" includes underwater sabotage, anonymous cyber attacks, disinformation campaigns, and non-military tactics to destabilise adversaries.

In December 2024, Finnish police said they were investigating whether a Russian ship was involved in the sabotage of an electricity cable running between Finland and Estonia.

A month earlier, the German government said damage to two undersea cables in the Baltic Sea looked like an act of sabotage. A cable between Finland and Germany was cut, as well as another cable between Lithuania and Sweden's Gotland Island. (BBC)

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