Beijing/Sydney  - China has formally arrested four employees of Anglo-Australian mining giant Rio Tinto on charges of trade secrets infringement and bribery, state media reported Wednesday.

The four employees - Australian citizen Stern Hu and Chinese nationals Liu Caikui, Ge Minqiang and Wang Yong - "obtained commercial secrets of China's steel and iron industry through improper means, which had violated the country's criminal law," the Xinhua news agency reported, citing an official statement.

Prosecutors claimed to have evidence that the four were involved in bribery, the report said, adding that there were suspects within China's steel and iron enterprises who had provided them with commercial secrets.

The four have been in detention since early July. Some reports suggested they could be charged with the more serious crime of violating state secrets.

The arrests came days after an editorial by Jiang Ruqin, an employee with the Jiangsu Province Administration for the Protection of State Secrets, accused Rio of cheating it out of 102 billion dollars over six years through stealing state secrets and bribing officials to get a higher price for its iron ore exports.

The detention of Hu has stressed bilateral relations and worried foreign investors in China.

In a statement earlier this week, Rio iron ore chief executive Sam Walsh said there was no evidence to support the detentions.

"We are still not aware of any evidence that would support their detention," he said. "Rio Tinto is committed to high standards in business integrity and takes its ethical responsibilities very seriously."

Australian consular officials visited Chinese-born Hu earlier this week and reported him well.

"We are pleased to hear that Stern appeared well and that he raised no welfare or medical concerns," Walsh said. Chinese law forbade the consular officials from discussing Hu's case with him.

Meanwhile, Rio has removed several staff from its Shanghai office, and there are concerns about how the arrests might affect its multi- billion dollar sales to China. (dpa)