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 coast guard said.

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

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."

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.

Taiwan has 14 international underwater cables and 10 domestic ones.

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 earlier 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.

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

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

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CHUNGHWA TELECOM