Four people working for Taiwanese tech giant Foxconn in China have been detained, Taipei said Friday, describing the circumstances as “quite strange”.

The employees were detained by public security in the central city of Zhengzhou for the equivalent of “breach of trust” under Taiwan law, Taipei’s top China policy body, the Mainland Affairs Council, said in a statement to AFP.

“The circumstances surrounding this case are quite strange,” the council said.

Foxconn “has declared the company suffered no losses, and the four employees did not harm the company’s interests in any way,” it said, without providing details about when they were detained or their roles.

Foxconn, also known by its official name Hon Hai Precision Industry, is the world’s biggest contract electronics manufacturer and assembles devices for major tech companies, including Apple.

Most of its factories are in China, including Zhengzhou, which is dubbed “iPhone City” as the home of the world’s biggest factory for the smartphone.

The Straits Exchange Foundation, a semi-official body in Taiwan handling people and business exchanges with China, told AFP the four detainees were Taiwanese.

The case “may involve corruption and abuse of power by a small number of public security officials, which has severely damaged business confidence,” the Mainland Affairs Council said.

“We urge the relevant authorities across the strait to investigate and address the matter promptly.”

A Foxconn spokesman declined to comment when contacted by AFP. China’s foreign ministry spokeswoman Mao Ning said she was “not aware of the specific situation”.

China and Taiwan have been locked in a decades-long dispute, with Beijing claiming the self-ruled island as part of its territory, which the Taipei government rejects.

Many Taiwanese companies set up factories in China over the past four decades, taking advantage of the shared language and cheaper operating costs, but investment has fallen sharply in recent years over regional tech disputes.