It is the latest in a series of Taiwanese undersea cable breakages, with previous incidents blamed on natural causes or Chinese ships.

Taiwan's Chunghwa Telecom reported the cable between Penghu, a strategic island group in the sensitive Taiwan Strait, and Taiwan was disconnected early Tuesday, the Ministry of Digital Affairs said.

The Togolese-registered ship Hongtai was intercepted in the area and escorted back to Taiwan, the coast guard said.

The case was being "handled in accordance with national security-level principles", it added.

"Whether the cause of the undersea cable breakage was intentional sabotage or a simple accident remains to be clarified by further investigation."

The Hongtai, using a flag of convenience, was crewed by eight Chinese nationals and had Chinese funding, the coast guard said.

Flags of convenience allow shipping companies to register their vessels in countries to which they have no link -- for a fee and freedom from oversight.

Beijing claims Taiwan as part of its territory and has threatened to use force to bring it under its control.

And Taiwan fears China could sever its communication links as part of an attempt to seize the island or blockade it.

"It cannot be ruled out that it was a grey zone intrusion by China," the coast guard said, referring to actions that fall short of an act of war.

"The coast guard will cooperate with the prosecutors in the investigation and make every effort to clarify the truth."

- High strategic value -

Taiwan has 14 international underwater cables and 10 domestic ones.

The ministry ordered Chunghwa Telecom to transfer voice communications and internet services for Penghu to other undersea cables.

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.

There is growing concern in Taiwan over the security of its cables after a Chinese-owned cargo ship was suspected of severing one northeast of the island this year.

Separately, two ageing subsea cables serving Taiwan's Matsu archipelago stopped functioning last month, with the outages blamed on "natural deterioration".

In February 2023, two subsea telecoms lines serving Matsu were cut within days of each other, disrupting communications for weeks.

Locals and Taipei officials suspected that Chinese fishing vessels or sand dredgers, which often drop anchor or scrape the seabed in Taiwanese waters, may have been responsible.

The Taiwanese coast guard identified last month 52 "suspicious" Chinese-owned ships flying flags of convenience from Mongolia, Cameroon, Tanzania, Togo, and Sierra Leone for close monitoring.

The stricter regime involves watching for anomalies in a ship's automatic identification system operation and fake vessel names.

Vessels suspected of loitering or anchoring near subsea cables will be warned by radio to leave the area, and boarding inspections carried out when needed.

AFP does not know yet if Hongtai is among the 52.

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