(CNN) -- An Australian employee of Rio Tinto, the world's second-largest mining company, is being held in China on suspicion of espionage and stealing state secrets, the Australian foreign minister said Wednesday.
Australia's Foreign Minister Stephen Smith expressed his surprise at China's actions.
The man, identified by the Australian government as Stern Hu, has been held along with three Chinese co-workers since Sunday, Foreign Minister Stephen Smith said.
He said the reason for Hu's detention "came as a surprise" to the Australian government.
"We've raised our concerns with the Chinese Embassy in Canberra," said opposition leader Malcolm Turnbull. "This is a matter of very real concern and it is completely unacceptable."
A Rio Tinto spokesman also referred to the charges as "surprising."
"We are not aware of any evidence that would support such an investigation," spokesman Nick Cobban told CNN.
"We will continue to work to support our employees and their families."
A spokesman at the Chinese government press office in Shanghai said they were aware of the story but could not confirm the arrest.
All four are employees at Rio Tinto's Shanghai office, the company said.
Australia's consular agreement with China allows for Australian officials to have access to Hu by Friday, Smith said. Officials have asked that Hu's wife and Rio Tinto officials be allowed to see him, Smith said.
The incident comes after Rio Tinto broke away from a $19.2 billion investment deal with state-owned Chinalco last month.
The deal with Chinalco was signed in February and was awaiting a review by Australia's Foreign Investment Review Board. The Chinalco-Rio Tinto deal soured as opposition party members ratcheted disapproval, claiming it put Australian resources at strategic risk.
Others saw the deal as a strategic alliance that would help further link resource-rich Australia with the commodities-hungry Chinese market.
Smith brushed aside speculation that the detentions are linked to the deal.
"I've seen no evidence and I have no basis for any such speculation," he said. "But I do underline that when our officials were advised of the reasons for the detention, that came as a surprise to us, as it came as a surprise to Rio Tinto, Mr. Hu's employer."
CNN's Kevin Voigt in Hong Kong, China, and Kendra Petersen in London, England, contributed to this report.
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