Rio Tinto says it is "very concerned" about its four employees detained in Shanghai amid accusations of bribery and spying.
The company said on Friday the accusations are "wholly without foundation".
Stern Hu, an Australian, and three other employees were detained in China last week amid negotiations about iron ore prices.
The incident has cast a shadow on relations between Australia and China.
Iron ore division chief executive Sam Walsh said the company believes they "acted at all times with integrity" and "in accordance with" Rio Tinto's code of ethical behaviour.
The company said it continued to operate in China and is maintaining iron ore shipments from Australia.
Earlier this week, China extended its investigations into what it calls spying and bribery by Rio Tinto employees to executives at five Chinese steelmakers.
The BBC reports officials at Baosteel Group, Anshan Iron & Steel Group, Laigang Group and Jigang Group are being questioned.
In June, Rio scrapped a $US19.5 billion deal with the state-owned Chinalco in favour of a tie-up with BHP Billiton.
