The Baltic Sea region is on high alert after several power cables and telecommunications links have been damaged in recent weeks and months, with some nations believing it is a series of sabotage attacks.
This week, the NATO military alliance boosted its presence in the area with frigates, aircraft and naval drones.
Several police investigations within the Baltic nations are underway but no suspects have been brought to trial.
There also are fears that Russia could target cables as part of a wider campaign of so-called "hybrid warfare" to destabilise European nations helping Ukraine.
German Chancellor Olaf Scholz said he and the Danish prime minister would continue talks on security in the Baltic Sea in Berlin adding that recent incidents in the area were a sign of the ongoing threat posed by Russia.
"Yesterday there was another report that another submarine cable had been damaged," he said.
"This shows the threat posed by the Russian shadow fleet."
Danish Prime Minister Mette Frederiksen said that Europe must boost its security and defence to counter Russian and Chinese influence on the European continent.
"We see Russian hybrid attacks in Europe, in the Baltic Sea… We need a stronger and more resolute Europe standing increasingly in its own right," she said.
Sweden launches sabotage investigation
The most recent incident saw an undersea power cable damaged between Sweden and Latvia on Sunday.
Swedish authorities chased and then boarded a Maltese-flagged ship seized in connection with the incident and began an investigation into the matter, the country's security police said.
The cable was damaged within Sweden's exclusive economic zone, likely as a result of external influence, Latvian officials said.
The investigation, which is ongoing, will determine whether or not the cable was sabotaged, Swedish authorities said.
Vezhen, the bulk carrier that has been seized, belongs to Bulgarian shipping company Navigation Maritime Bulgare.
The head of the Bulgarian company, Captain Aleksandar Kalchev, said the Vezhen might have struck the Baltic undersea cable when one of the ship's anchors dropped to the seabed in high winds.
He added that there was no malicious intent.
"[The crew] have been instructed to assist authorities and the situation never escalated and it is calm at the moment," he told Reuters, adding the crew had been initially held at gunpoint.
A spokesperson from Sweden's Meteorological and Hydrological Institute said there were winds of about 8-10 metres per second outside Gotland in the early hours of Sunday.
"That's not very strong wind. It's well below the 14 metres per second that is the threshold for a gale warning," the spokesperson said, adding that waves were not very high, either.
NATO boosts military presence
The NATO alliance is ratcheting up its guard against suspected attempts to sabotage underwater energy and data cables and pipelines that crisscross the Baltic, prompted by a growing catalogue of incidents that have damaged them.
"We will do everything in our power to make sure that we fight back, that we are able to see what is happening and then take the next steps to make sure that it doesn't happen again. And our adversaries should know this," NATO Secretary-General Mark Rutte said this month in announcing a new alliance mission, dubbed "Baltic Sentry," to protect the underwater infrastructure vital to the economic well-being of Baltic-region nations.
Without specifically blaming Russia, Mr Rutte said "hybrid means sabotage".
"Hybrid means cyber-attacks. Hybrid means sometimes even assassination attacks, attempts, and in this case, it means hitting on our critical undersea infrastructure," he added.
Finnish police suspect that the Eagle S, an oil tanker that damaged the Estlink 2 power cable on December 25, is part of Moscow's "shadow fleet" used to avoid war-related sanctions on Russian oil exports.
Despite the increased NATO presence and growing concerns, several Western intelligence officials think it could be accidental damage.
Speaking on condition of anonymity because of the sensitive nature of their work, one Western intelligence official told The Associated Press that recent damage was most likely caused by anchors being dragged by ships that were poorly maintained and poorly crewed.
One senior intelligence official told AP that ships' logs and mechanical failures with ships' anchors were among "multiple indications" pointing away from Russian sabotage.
ABC/Wires
