Four employees from Rio Tinto PLC's (RTP) Shanghai-based iron ore team have been detained since Sunday by Chinese authorities, though the company doesn't know why they are being held, company officials said Tuesday.

"The reasons for these actions are unclear. Rio Tinto intends to cooperate fully with any investigation the Chinese authorities may wish to undertake and has sought clarification on what has occurred," the Anglo-Australian miner said in a statement.

Rio Tinto in its statement did not provide names or nationalities of the employees, but a Rio Tinto official in Beijing, who declined to be named, said one Australian, Stern Hu, and three others from Rio's iron ore marketing department had been detained.

Hu is general manager for China operations at Rio Tinto's iron ore division, according to Rio's Web site.

A senior official at Rio's China operation, who also declined to be named, said it is "not clear why the government is holding our employees," but noted that in China authorities can hold an individual without giving any reason for 72 hours. The company had not been able to make contact with the employees since they were detained on Sunday, London-based Rio Tinto spokesman Nick Cobban said.

"Rio Tinto is concerned about the employees' well-being and is doing everything possible to help them and support their families," the company said.

Rio Tinto maintains offices in Shanghai, Beijing and Guangzhou, China, according to the company's Web site.

Rio's China operations are focused largely on sales and marketing to major customers in the nation. China is Rio's biggest market for iron ore.

Rio last month walked away from a $19.5 billion alliance with Aluminum Corp. of China, or Chinalco, in favor of a rights issue and iron ore joint venture with Anglo-Australian BHP Billiton Ltd. (BHP) to pay down debt.

Some officials in China reacted bitterly to the spurning of Chinalco's investment.

Rio's iron ore team is negotiating annual contract prices with Chinese steel mills.

China's steel association has insisted on a cut of at least 40% from last year's contract price. But major Japanese and Korean steelmakers have already reached separate iron-ore supply contracts based on price cuts of 28% to 33%, a figure that Rio considers the benchmark for the industry.

Company Web site: www.riotinto.com

-By Jeffrey Sparshott, Dow Jones Newswires; +44 (0)207 842 9347; jeffrey.sparshott@dowjones.com