Swedish authorities seized and boarded a ship on Sunday just hours after it was suspected of sabotaging a communications cable in the country’s exclusive economic zone beneath the Baltic Sea.

The Vezhen, a cargo ship, is suspected to have damaged a cable owned by the Latvian State Radio and Television Centre (LVRTC) running between the Latvian city of Ventspils and the Swedish island of Gotland.

In an announcement on Sunday, the public prosecutor’s office said a “preliminary investigation into suspected serious sabotage has been initiated,” and confirmed the investigation was being led by the country’s Security Service (SÄPO).

SÄPO spokesperson Johan Wikstrom confirmed that “persons from Swedish authorities have been on board the vessel to carry out investigative measures.”

It follows heightened concern regarding disruptions to subsea infrastructure in the wake of another incident in the Baltic Sea on Christmas Day, when a ship dragged its anchor for almost 100 kilometers (62 miles) severing a number of cables.

Authorities in Finland have seized that ship, the Eagle S, after it was boarded by armed officers via helicopter, and said this week they suspect the damage was done intentionally. Those comments followed reports citing anonymous intelligence officials that the cable breakages were assessed to be accidents rather than acts of sabotage.

Two weeks ago, NATO allies bordering the Baltic Sea, including Sweden and Latvia, issued a statement warning they reserved the right to take action against Russian ships that threaten submarine infrastructure. The alliance also announced Baltic Sentry, described as “new military activity” to “enhance NATO's military presence in the Baltic Sea.”

Sweden’s senior public prosecutor, Mats Ljungqvist, said on Sunday: “We are now carrying out a number of concrete investigative measures, but I cannot go into what they consist of due to the ongoing preliminary investigation.

“Several authorities, including the National Police Operations Department, the Coast Guard and the Armed Forces, are involved in the investigation. I can state that Swedish authorities are now working intensively and jointly to investigate this incident,” he added.

LVRTC said it “continues to provide services via alternative data transmission routes” and that while “there may be delays in data transmission speeds, but for the most part, this does not impact end users in Latvia.”

According to the Latvian navy, the Vezhen is one of three ships that were being investigated over the incident. The cargo ship was escorted to an anchorage point near Sweden’s Karlskrona naval base as investigations continue.