Swedish prosecutors said Monday they had closed a probe into a Bulgarian ship that severed a Baltic Sea cable linking Sweden and Latvia in January, ruling it an accident but noting the vessel had several technical faults.

Swedish authorities had seized the Malta-flagged Vezhen when damage to the underwater fibre-optic cable linking the Swedish island of Gotland to Ventspils in Latvia was discovered on January 26.

Prosecutors in February ruled out sabotage and released the ship.

"The investigation clearly shows that the cable break was caused by a combination of harsh weather, technical deficiencies, and suspected lack of seamanship on the vessel in question," senior prosecutor Mats Ljungqvist said in a statement. "The investigation shows that it was an accident."

The Vezhen's black box was analysed, several people were questioned, and video footage showing how the cable was broken was examined, the prosecution authority said.

On the night in question, the weather conditions were bad, with heavy seas in the Baltic.

The ship's anchor would normally have been secured by three independent safety devices. But two of them had been out of order "for some time", the probe showed.

The only functioning device holding the anchor in place broke after it was hit by a big wave on January 25 at 4:11 am, it said.

As a result, the anchor and chain were fully released, causing the ship to slow and gradually turn.

"Since the ship's autopilot was engaged at the time, the autopilot compensated for this. No alarm notified the person on the command bridge about what had happened," the prosecution authority said.

The next day the ship sailed over the cable off of Gotland, and its dragging anchor severed it.

"We can therefore conclude that the cable was not damaged intentionally," Ljungqvist said.

The conclusions were submitted in the spring of 2025 to Latvian authorities, who are conducting their own investigation.

Political leaders and experts had at the time suggested the incident was part of a "hybrid war" conducted by Russia against Western countries against the backdrop of tensions over Moscow's full-scale invasion of Ukraine.

Sweden closes probe into Latvia cable damage