Taiwanese prosecutors have formally charged the captain of a Chinese-crewed cargo ship that Taipei says severed one of its subsea cables earlier this year.

The Togo-flagged Hong Tai 58 was detained by Taiwan’s coastguard in February near the site of a cable breakdown amid allegations that it had deliberately dropped its anchor to cause damage.

The ship’s captain, who was only identified to the public by his surname Wang, was charged on Friday with being responsible for the incident, the prosecutors said.

Seven Chinese nationals who were on board the ship will not be charged, and will be transported back to China, the prosecutors added.

The case marks a first for Taiwan, where subsea cables have become the latest front in what is described as “hybrid warfare” or “grey zone activity” with China. The terms refer to low-grade coercive acts such as sabotage that hold a certain degree of plausible deniability.

China has long claimed Taiwan, an island with a population of 23 million, as a province of the mainland and has threatened to annex it by force, if necessary.