By Andrius Sytas

VILNIUS, Jan 4 (Reuters) - An undersea telecoms cable was damaged in the Baltic Sea on Friday and Latvian investigators on Sunday boarded a ship in connection with the incident, the country's state police said in a statement.

The Baltic Sea region is on high alert after a string of power cable, telecom link and gas pipeline outages since Russia invaded Ukraine in 2022, and the NATO military alliance has boosted its presence with frigates, aircraft and naval drones.

Lithuania's National Crisis Management Centre said the cable runs from Sventoji in Lithuania to Liepaja in Latvia, two coastal towns some 65 km (40 miles) apart, and that it was not immediately clear what caused the incident.

"At this time, neither the vessel nor its crew is detained, they are cooperating with the police, and active work continues to clarify the circumstances," Latvian police said on X.

Latvia's Prime Minister Evika Silina said the damage had occurred near Liepaja.

"The incident has not affected Latvian communications users," she wrote on X.

The latest incident is made public five days after Finnish police seized a cargo vessel en route from Russia to Israel on suspicion of sabotaging an undersea telecoms cable running from Helsinki across the Gulf of Finland to Estonia.

(Reporting by Andrius Sytas, additional reporting by Anna Ringstrom, writing by Terje Solsvik, editing by Gwladys Fouche)