Taiwan coast guard officials boarded a Chinese-owned freighter and detained its crew after an undersea cable near an outlying island was severed, Taipei authorities said Tuesday.

The detentions mark the first significant Taiwanese response to suspected Chinese undersea cable attacks around the self-ruled island.

Taiwanese telecommunications firm Chunghwa Telecom said a severed cable early Tuesday disrupted communications between the main island and Penghu, a strategic island near the Chinese coast in the Taiwan Strait.

The Taiwanese Ministry of Digital Affairs reported the outage.

Russia is suspected of causing similar undersea cable outages in the Baltic Sea. In November, a Chinese bulk carrier sailed over two cut cables, and a Hong Kong-flagged container ship is suspected of cutting another one a month earlier.

Those incidents disrupted the internet and other communications among several northern European states.

Analysts say cutting undersea cables is part of “gray zone” warfare operations, or military activities targeting adversaries that fall short of combat.

Details of how the latest Taiwanese cable was cut were not disclosed, and the coast guard said it was investigating.

Chinese Foreign Ministry spokesman Lin Jian told reporters that he was unaware of the incident and that Beijing did not consider it a matter related to foreign affairs.

Ships dragging anchors along the sea bottom have been blamed for severing communications lines.

The coast guard said in a statement that Taiwanese vessels intercepted and boarded the Togolese-registered cargo ship Hongtai, which was then escorted to Taiwan.

Focus Taiwan posted a video of the boarding on X, according to the official state news service CNA,

Authorities were dealing with the matter “in accordance with national security-level principles,” the statement said.

“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 statement said the Hongtai was using a flag of convenience and its voyage was financed by Chinese interests. Eight Chinese nationals crewing the ship were detained.

Flags of convenience allow shipping companies to register ships in foreign countries to avoid oversight.

“It cannot be ruled out that it was a gray zone intrusion by China,” the coast guard said. “The coast guard will cooperate with the prosecutors in the investigation and make every effort to clarify the truth.”

Retired Navy Capt. Jim Fanell, a former Pacific Fleet intelligence director, said China probably will take action in response to the crew detentions.

“I cannot see [Chinese President] Xi Jinping sitting back and accepting this boarding without some kind of larger response, akin to what they did at Scarborough in 2012, which could very well lead to an invasion,” Capt. Fanell said. “The proper U.S. response should be another Taiwan Strait transit, preferably by the USS Ronald Reagan.”

Capt. Fanell said in 2012 that the People’s Liberation Army lacked sufficient power in the South China Sea to impose its will, but the Obama administration took no action after the Chinese military began occupying and developing disputed islands. Eventually, the Chinese military built a series of island military bases near the Philippines, a U.S. ally, including Scarborough Shoal.

Today, the PLA has far greater military capabilities and capacities in the Taiwan Strait. The boarding of the cargo ship and detention of the Chinese crew represent an embarrassment for the PLA, he said, and thus a response is likely.

“Now Xi has to question whether or not he wants to roll the dice and start an invasion or make some kind of armed retaliatory act and risk what [President Trump] may do in response,” Capt. Fanell said.

Several undersea cables link Taiwan to the Penghu Islands, also known as Pescadores.

China has been stepping up its coast guard activities around the outlying Taiwanese islands in a bid to press its claim that Taiwan is part of China and to intimidate pro-independence forces in Taipei.

Taiwan’s government regards the island as a separate nation called the Republic of China.

Ou Yu-fei, a coast guard press spokesman, said the detained ship appears to have caused the cable damage.

The cargo ship was the only vessel in the area at the time of the transmission disruption, he said.

“We’re not ruling out the possibility that it was engaged in an act of sabotage. We go by the evidence. It’s too early to reach conclusions,” Mr. Ou told The New York Times.

He said the ship was suspected of using a false registration number and had changed its name.

The coast guard had been monitoring the ship since Saturday and ordered it to leave the area.

“It is possible that it used the time when it was leaving to carry out sabotage,” Mr. Ou said.

Another cable was damaged in January near northern Taiwan, where several undersea cables come ashore.

Taiwanese authorities said they believe a Chinese ship dragged its anchor over the cable to cut it.

• Bill Gertz can be reached at bgertz@washingtontimes.com.