The Swedish authorities on Monday boarded a ship in connection with what they described as “gross sabotage” after an undersea communications cable in the Baltic Sea was damaged a day earlier. The ship was escorted to the coast of Sweden for an investigation, the authorities said.
“We suspect that a serious act of sabotage was committed in the Swedish economic zone yesterday,” Mats Ljungqvist, the Swedish prosecutor leading the investigation into the damage, said in a phone interview on Monday.
The authorities have not yet made public the nature or the extent of the damage to the communications cable, which runs between Sweden and Latvia.
The incident follows other suspected sabotage attempts on cables under the Baltic Sea, which has recently become a theater of potential hybrid warfare between NATO and Russia.
Two weeks ago, the Atlantic alliance started a new patrol and surveillance operation to protect critical infrastructure in the sea, on which Russia has coastline, after a number of cables were severed.
The NATO mission, called Baltic Sentry, is intended to help protect underwater cables and pipelines by enhancing the alliance’s presence in the region, said Mark Rutte, the organization’s secretary general. The operation involves frigates, maritime patrol aircraft, submarine satellites, remotely operated vehicles and drones.
NATO, of which Sweden is the newest member, said the mission was an effort “to improve the ability to protect critical undersea infrastructure and respond if required.”
Alliance officials have regularly said that, while they suspect Russia of being behind the sabotage of cables and pipelines, actual responsibility is extremely difficult to prove.
The Swedish security service said a preliminary investigation suggested that the incident on Sunday may have been an effort to target Swedish interests. The seized vessel “is suspected to have carried out the sabotage” the security service said in a statement issued Monday.
“Right now, Swedish authorities are on the vessel to conduct various investigative measures,” Johan Wikstrom, a spokesman for the service, said by telephone on Monday.
Mr. Ljungqvist, the prosecutor, said that the seized vessel was called the Vezhen.
Navigation Maritime Bulgare, a Bulgarian shipping company that lists the Vezhen in its fleet as a bulk carrier with a Maltese flag, posted a statement on its website on Monday referring to a “a force majeure situation that occurred due to the unfavorable hydrometeorological conditions in the area.”
The company said it did not have “information about any intentional actions by the crew” that could lead to cable damage and expressed its support for the authorities in the investigation.
Mr. Wikstrom said the coast guard on Sunday escorted the vessel to the Swedish coast. It is now anchored outside of Karlskrona, a southern city that is home to Sweden’s largest naval base and also the coast guard headquarters.
Mr. Wikstrom declined to provide other details about the seized vessel or how and where the authorities had discovered the damage to the cable.
NATO ships and aircraft responded to the reported damage and were working with their regional allies, the alliance said on Monday in an email.
Prime Minister Evika Silina of Latvia said in a social media post that Latvian, Swedish and NATO authorities were working together to investigate the incident, patrol the area and inspect vessels. She added that the cable had been damaged in Sweden’s economic zone and that the authorities had started a “criminal investigation.”
In late December, the Finnish authorities seized an oil tanker that they suspected of cutting undersea cables, accusing the ship of being part of Russia’s “shadow fleet,” which Western officials say they think Russia uses to evade sanctions. In response, NATO said it would increase security in the region and the European Union threatened new sanctions against Moscow.
In November, several European countries halted a Chinese commercial ship after two fiber-optic cables were severed. Germany’s defense minister described the severing of the cables as an act of “sabotage” aimed at European countries that have supported Ukraine while it fights Russia, though American intelligence authorities said they were not cut deliberately.
In 2022, explosions damaged parts of the Nord Stream pipeline, stopping Russian natural gas deliveries to Western Europe. American intelligence pointed to a pro-Ukrainian group, although much remains murky about the incident.
The cable that was damaged on Sunday belonged to Latvia’s state-run radio and television center, according to a statement from the center on Sunday night.
The statement noted that, since the cable lies at a depth of more than 160 feet, the center would be able to determine the exact nature of the damage only once the repair work began.
Steven Erlanger contributed reporting from Berlin.