TAIPEI, Taiwan (AFP) — 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 (MAC), said in a statement to Agence France-Presse.

“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, their nationalities 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 Agence France-Presse (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 MAC said.

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

A Foxconn spokesperson declined to comment when contacted by AFP. China’s foreign ministry did not immediately respond to AFP’s request for comment.

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.

Despite the tensions, Taiwanese companies have flocked to mainland China in the past 40 years to set up factories, taking advantage of the shared language and cheaper operating costs.