Chinese police have detained four workers of the Taiwanese iPhone maker, Foxconn, in circumstances Taipei has described as “strange”.

The employees were arrested in Zhengzhou in Henan province on “breach of trust” charges, Taiwan’s Mainland Affairs Council said in a statement.

The BBC has contacted Foxconn for comment.

The company is the biggest maker of iPhones for US technology giant Apple and is one of the largest employers in the world, with major manufacturing facilities in China.

Taiwanese authorities suggested the detentions may be a case of “abuse of power” by Chinese police officers and said the case undermines the confidence of businesses operating in China.

A Chinese Foreign Ministry spokesperson said they were not aware of the matter.

In October last year, China’s tax and land authorities launched an investigation into the company.

At that time, Foxconn’s founder Terry Gou was running as an independent candidate in Taiwan’s presidential election.

Taiwan has urged its citizens to “avoid non-essential travel” to the mainland as well as Hong Kong and Macau after China unveiled guidelines in June detailing criminal punishments for what Beijing described as diehard “Taiwan independence” separatists.

Foxconn’s facility in Zhengzhou is the world’s largest iPhone factory which is widely known as “iPhone City”.

Despite a long-standing geopolitical rift between Beijing and Taipei, Foxconn is among many Taiwanese businesses that have built factories in China.

Beijing sees the island as a breakaway province that will, eventually, be part of the country, and has not ruled out the use of force to achieve this.

But many Taiwanese consider themselves to be part of a separate nation – although most are in favour of maintaining the status quo where Taiwan neither declares independence from China nor unites with it.