SEOUL, South Korea – Tensions in the waters off a tripwire Taiwanese island close to China’s coast are spiraling this week as China intercepted and boarded a Taiwanese vessel, Coast Guard units confronted each other and the Biden administration appealed for calm.

Analysts say Kinmen, a Taiwanese-controlled island less than two miles off from mainland China, provides ideal terrain for Beijing’s “grey zone” tactics: Navigation limits are poorly demarcated and its waters are allegedly the site of illegal activities.

On Monday, Chinese Coast Guards boarded a Taiwanese sightseeing boat off Kinmen and conducted an approximately 30-minute inspection. Passengers told local media how frightening the incident was. A day later, Taiwanese Coast Guard vessels pursued a Chinese Coast Guard craft that they claimed had entered the island’s restricted waters.

“We are closely monitoring Beijing’s actions, we continue to urge restraint and no unilateral change to the status quo,” State Department spokesman Matt Miller told reporters in Washington Tuesday. “We urge [China] to engage in meaningful dialogue with Taiwan to reduce the risk of miscalculation.”

While Washington urges calm, Taipei has pushed back against China’s account of the incident last week which sparked the latest round of confrontations. On Feb. 14, Taiwan’s Coast Guard chased a Chinese speed boat in restricted waters around Kinmen. The pursuit ended when the vessel capsized, leading to the drowning death of two Chinese sailors and the arrest of two other crewmembers by Taiwan’s Coast Guard.

Over the weekend, an angry China, calling the boat a fishing craft, announced it would cease to respect a demarcation line unilaterally established around Kinmen by Taipei, a line that has been unofficially observed by both sides since the early 1990s. Beijing also announced it would step up Coast Guard activities in the area, setting the stage for this week’s encounters.

Taiwan’s ruling Democratic Progressive Party sharply disputes Beijing’s narrative. In a series of tweets on X, Wen Lii, the DPP’s director of international affairs, called the two drowning deaths “regrettable,” but added: “The Chinese boat evicted by Taiwan’s Coast Guard fits the description of ‘3 Nos’: No ship name, No ship certificate, No registered port.”

That makes the boat’s location illegal in both China and Taiwan, the post said. Photos of the vessel published in Taiwanese media show an approximately five-meter skiff sporting dual outboard motors.

Many of China’s “3 No” vessels are “involved in illegal fishing, smuggling or human trafficking,” the DPP spokesman added, noting that island authorities “have expressed these problems time and again to Chinese authorities, to limited effect. With sporadic, uneven law enforcement and speculation of corruption, China seems unable to rein in these illicit ships.”

The two Chinese survivors of last week’s clash returned to China Tuesday, according to mainland press reports, accompanied by representatives of the Red Cross Society of China in Fujian.

A U.S. analyst said Taiwan’s account sounded more plausible.

“It was a tiny little boat … running from the cops, so to call it a ‘fishing’ boat is probably a stretch,” said Drew Thompson, an ex-director for China, Taiwan and Mongolia in the office of the U.S. Secretary of Defense. “The reality is Chinese and Taiwanese coastal waters have been kind of fished out, so that boat may have been pursuing alternative revenue streams such as trafficking or smuggling goods.”

Taiwan has its own issues. Faced with a declining population, the country relies on some 700,000 migrant workers to do much of the country’s manufacturing and nursing work, including an underground economy populated by illegals.

“Traffickers subject foreign men and women to forced labor and sex trafficking in Taiwan,” the State Department, which considers Taiwan a “Tier 1” risk country for trafficking, wrote in a 2023 report.

The sea is an obvious route for illegal migrants — as well as for illegal goods.

“There has been some degree of tolerance on both sides of the Strait for smuggling activities: cigarettes, alcohol, and people,” said Mr. Thompson, currently a senior research fellow at the University of Singapore. “Rather than addressing the possible criminality of the skiff, Beijing is making it a political issue.”

The creep of Chinese vessels ever closer to Kinmen could have a psychological impact in Taipei. Experts believe any invasion of Taiwan proper would be preceded by a Chinese takeover of the island. And with Beijing vowing to ignore the de facto demarcation line around Kinmen, risks are rising.

“Such actions risk unintentional clashes and an unnecessary escalation of tensions in the Taiwan Strait,” the DPP post warned.

Even so, Taiwan, too, has admitted some culpability.

Taiwan News reported that the Coast Guard’s failure to capture video of last week’s boat chase and to present “key facts” of the encounter, including multiple collisions before the Chinese boat capsized, “had aroused suspicions from the victims’ family members and the public.”

The situation presents a challenge for Taiwan’s President-elect William Lai, who takes office on May 20. In January’s election, Mr. Lai led the Democratic Progressive Party, the island’s most anti-Beijing major political party, to an unprecedented third term.

Mr. Lai is currently visiting Japan, which has close ties to Taiwan.

• Andrew Salmon can be reached at asalmon@washingtontimes.com.