Taiwan’s coast guard detained a cargo ship and its Chinese crew on Tuesday and said it was investigating whether the vessel had deliberately cut an undersea telecoms cable in the latest possible breach of the island’s communication lines.

The island’s coast guard said the incident is a national-security matter and possible case of Chinese sabotage.

Taiwan, which China claims as its own territory, has repeatedly complained about "grey zone" Chinese activities around the island, designed to pressure it without direct confrontation, such as balloon overflights and sand dredging.