China vowed  to punish “diehard” Taiwan politicians, saying it would ban several from visiting the mainland, as tensions between Beijing and Taipei spiked to their highest level in years.

China claims Taiwan as its territory — to be seized one day, by force if necessary — and has intensified efforts in recent years to isolate the self-ruled island on the international stage.

On Friday, the Taiwan Affairs Office in Beijing warned that “the mainland will pursue criminal responsibility for Taiwan independence diehards in accordance with the law, to be effective for life”.

The statement by spokeswoman Zhu Fenglian named Taiwanese Premier Su Tseng-chang, parliament speaker Yu Shyi-kun and Foreign Minister Joseph Wu as among a minority of independence supporters.

Zhu said the politicians “have tried to instigate cross-strait confrontation, maliciously attacked and slandered the mainland… severely undermining cross-strait relations”.

She added that Beijing has prohibited them and their family members from entering the mainland, Hong Kong or Macau.

Their affiliates would also be restricted from cooperating with mainland organisations and individuals, she said, without giving more details.

Taiwan’s Su on Friday brushed off the threat from Beijing, saying he “won’t be intimidated.”

“It doesn’t (rule) Taiwan for one day but it’s bossing Taiwan around,” Su said of Beijing when asked about the list of “diehards” in parliament.

The nationalist Kuomintang party fled to Taiwan in 1949 after losing the Chinese civil war.

The island of 24 million people has since transformed into a vibrant democracy and major tech hub, leading many — including President Tsai Ing-wen — to assert Taiwan’s distinct identity, which Beijing attacks as separatism.

Beijing-Taipei ties have plunged since Tsai rose to power in 2016.

“Those who forget their ancestors, betray their motherland and split the country will not come to a good end,” Zhu said.

The comments came a day after the head of a visiting European Parliament delegation to Taipei called Taiwan’s democracy “a treasure” to be protected, promising to stand with the island.

China has dramatically ramped up military activities in recent years, with a record number of planes intruding into the island’s air defence identification zone (ADIZ) in early October.