By Andrius Sytas and Johan Ahlander
STOCKHOLM/VILNIUS (Reuters) -An undersea fibre optic cable between Latvia and Sweden was damaged on Sunday, likely as a result of external influence, Latvia said, prompting NATO to deploy patrol ships to the area and triggering a sabotage investigation by Swedish authorities.
Sweden's Security Service has seized control of a vessel as part of the probe, the country's prosecution authority said.
"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," senior prosecutor Mats Ljungqvist said in a statement.
NATO was coordinating military ships and aircraft under its recently deployed mission, dubbed "Baltic Sentry". The effort follows a string of incidents in which power cables, telecom links and gas pipelines have been damaged in the wake of Russia's invasion of Ukraine in February 2022.
Latvian Prime Minister Evika Silina said her government was coordinating with NATO and other countries in the Baltic Sea region to clarify the circumstances surrounding the latest incident.
"We have determined that there is most likely external damage and that it is significant," Silina told reporters following an extraordinary government meeting.
Latvia's navy said earlier on Sunday it had dispatched a patrol boat to inspect a ship and that two other vessels were also subject to investigation.
Up to several thousand commercial vessels make their way through the Baltic Sea at any given time, and a number of them passed the broken cable on Sunday, data from the MarineTraffic ship tracking service showed.
One such ship, the Malta-flagged bulk carrier Vezhen, escorted to Swedish waters by a Swedish coastguard vessel on Sunday evening, MarineTraffic data showed. It later anchored outside the Swedish naval base in Karlskrona in southern Sweden.
It was not immediately clear if the Vezhen, which passed the fibre optic cable at 0045 GMT on Sunday, was subject to investigation.
A Swedish coastguard spokesperson declined to comment on the Vezhen or the position of coastguard ships.
Bulgarian shipping company Navigation Maritime Bulgare, which listed the Vezhen among its fleet, did not immediately reply to requests for comment outside of office hours.
NATO COOPERATION
Swedish navy spokesperson Jimmie Adamsson earlier told Reuters it was too soon to say what caused the damage to the cable or whether it was intentional or a technical fault.
"NATO ships and aircrafts are working together with national resources from the Baltic Sea countries to investigate and, if necessary, take action," the alliance said in a statement on Sunday.
Swedish Prime Minister Ulf Kristersson said his country was cooperating closely with NATO and Latvia.
NATO said last week it would deploy frigates, patrol aircraft and naval drones in the Baltic Sea to help protect critical infrastructure and reserved the right to take action against ships suspected of posing a security threat.
Finnish police last month seized a tanker carrying Russian oil and said they suspected the vessel had damaged the Finnish-Estonian Estlink 2 power line and four telecoms cables by dragging its anchor across the seabed.
Finland's prime minister in a statement said the latest cable damage highlighted the need to increase protection for critical undersea infrastructure in the Baltic Sea.
The cable that broke on Sunday linked the Latvian town of Ventspils with Sweden's Gotland island, and was damaged in Sweden's exclusive economic zone, the Latvian navy said.
Communications providers were able to switch to alternative transmission routes, the cable's operator, Latvian State Radio and Television Centre (LVRTC), said in a statement, adding it was seeking to contract a vessel to begin repairs.
"The exact nature of the damage can only be determined once cable repair work begins," LVRTC said.
A spokesperson for the operator said the cable was laid at depths of more than 50 metres (164 ft).
Unlike seabed gas pipelines and power cables, which can take many months to repair after damage, fibre optic cables that have suffered damage in the Baltic Sea have generally been restored within weeks.