The Cameroon-flagged vessel was intercepted by the coast guard on Friday after Taiwan's Chunghwa Telecom reported damage to a subsea cable.

The vessel, which is owned by a Hong Kong person and was crewed by seven Chinese nationals, was ordered to return to waters off Keelung port in northern Taiwan for inspection, the coast guard said in a statement.

But coast guard personnel were unable to board the ship due to rough seas and too much time had passed for the vessel to be held further, so it was allowed to sail for South Korea's Busan port.

Taiwan has asked South Korean authorities for assistance in the investigation into the ship, which also sails under the Tanzanian flag with two sets of automatic identification system signals, the coast guard said.

"An analysis of the ship's historical trajectory has yet to reveal its true intent," the coast guard said.

"However, the possibility of a Chinese-flag of convenience ship engaging in grey-zone harassment cannot be ruled out," it said, referring to tactics that fall short of an act of war.

China regards Taiwan as part of its territory and has threatened to use force to bring the self-ruled island under its control.

In recent years, Beijing has ramped up military pressure on Taipei, which fears China could sever communication links to the island as part of an attempt to seize it.

Chunghwa's telecoms service quickly returned to normal on Friday after it activated a back-up mechanism, the semi-official Central News Agency said.

In February 2023, two undersea telecoms lines serving Taiwan's outlying Matsu archipelago were cut, disrupting communications for weeks.

Taipei's Communications Commission and locals said at the time that Chinese fishing vessels or sand dredgers may have done the damage.

The world's data and communications are carried across oceans by great bundles of subsea fibre optic cables -- with their high strategic value making them potential targets for attack.

Sweden and Finland are investigating the cutting of a Baltic undersea cable in December, which Helsinki suspects was sabotaged by a Russian-linked vessel.

Two telecommunications cables were cut on November 17 and 18 in Swedish territorial waters.

A Chinese-flagged bulk carrier, the Yi Peng 3, which was above the area at the time, is suspected of involvement.

joy/amj/mtp

CHUNGHWA TELECOM