Taiwan detained the Chinese crew of a freighter after an undersea communications cable to one of its offshore outposts was severed, a move that risks heightening cross-strait tensions.

Taiwan’s Coast Guard said the eight crew and the Togolese-registered vessel were taken into custody on February 25. It added on February 26 that prosecutors have interviewed them.

The incident was being investigated to see if sabotage of the cable linking Taiwan’s main island and the smaller Penghu was involved, the Coast Guard said in its statement, adding that the freighter had lingered near the line crucial to internet connectivity. 

The government said it asked Chunghwa Telecom to use nearby cables to ensure communication remained open with Penghu Island, which sits about 50 kilometers (30 miles) west of Taiwan and 140 kilometers from China.

It is very rare for Taiwan to detain Chinese nationals over a severed cable, an issue that’s taking on more importance not only for the government in Taipei but around the world. In January, Taiwan said it suspected a Chinese-owned cargo vessel damaged an undersea cable near its northeastern coast. That episode followed another Chinese vessel’s suspected involvement in damaging data cables in the Baltic Sea in November.

When asked about the Penghu cable getting severed at a regular press briefing in Beijing, Chinese Foreign Ministry spokesman Lin Jian said he wasn’t familiar with the matter. 

The integrity of undersea cables has been a rising security issue for Taiwan, which China claims as its territory and has threatened to take with force if necessary. In 2023, telecom service in Taiwan’s Matsu Islands were disrupted for months after Chinese fishing vessels cut its cables.

That incident and other issues like earthquakes have spurred Taipei to accelerate plans to make the archipelago more resilient to communications breakdowns and direct attacks on its digital infrastructure.

China uses a range of tactics to intimidate the Taiwan government and make its job running the U.S.-backed democracy of 23 million people more difficult. Those efforts range from large-scale military maneuvers around the main island to online disinformation campaigns intended to convince the public that their leaders can’t resist Beijing’s campaign to take over.