An undersea fiber 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.