It follows the interception of the Da Jin Man 88 fishing boat by two mainland coastguard vessels late on Tuesday.

Mainland officers boarded the boat for inspection and instructed the Taiwanese captain and four crew members – one Taiwanese and three Indonesians – to head towards the mainland coastal city of Jinjiang in Fujian province.

The Taiwanese coastguard tried to intervene but backed off to prevent further escalation after the mainland sent seven vessels in two groups to block them.

03:03

Furious mainland China slams Taiwanese leader’s ‘blatant’ call for independence

Furious mainland China slams Taiwanese leader’s ‘blatant’ call for independence

Tsai said the incident was an “unusual case” and noted that the mainland had stated that the boat violated its fishing regulations.

He did not rule out the possibility that the detention was meant to put more pressure on Taipei’s administration but said further analysis was needed to determine whether it was part of a cognitive warfare operation by the mainland.

“Beijing may use the recent fishing-related seizure and potential subsequent administrative penalties as a means to demonstrate its jurisdiction over the Taiwan Strait, weaken the government’s sovereign status, or pressure the government,” Tsai said.

Taiwanese authorities acknowledged that the boat was operating within mainland waters during the ban.

“The incident involved a Taiwanese fishing boat operating in Chinese waters during China’s summer fishing moratorium. Consequently, the Chinese coastguard took law enforcement action,” Kuan Bi-ling, head of Taiwan’s Ocean Affairs Council, said in a statement late on Wednesday.

Kuan said the mainland coastguard had been more active in enforcing laws in waters near its coast. “Fishermen are advised to remain vigilant and take precautions to avoid similar incidents,” she said.

05:06

William Lai sworn in as new Taiwan leader amid pledge to keep status quo across the strait

William Lai sworn in as new Taiwan leader amid pledge to keep status quo across the strait

Analysts said the tone – focusing on the law enforcement nature of the action – was a departure from the previous confrontational “anti-China, protect Taiwan” rhetoric coming from the independence-leaning administration.

Local news reports said Washington encouraged the two sides to “continue to communicate with each other and resolve the issue peacefully”.

Wang warned that since the fault was on the Taiwanese side, any attempt by the Lai administration to escalate the dispute with the mainland could simply exacerbate the situation.

Chieh Chung, a professor of international relations and strategic studies at Tamkang University, said the detentions might be an attempt by Beijing to establish a new norm.

“It could pave the way for seizing Taiwanese civilian vessels in the future,” he said.

Chieh said the mainland announced in June 2022 that it asserted “rights, sovereignty, and jurisdiction over the Taiwan Strait”, a declaration that its coastguard could deploy as a legal basis for its actions.

“Our defence and security authorities must closely monitor developments, considering the potential impact on our civilian vessels, including supply ships hired by the military for transport, operating in the contested waters,” he warned.