Four Rio Tinto workers detained in China over espionage and bribery claims are facing nearly a year and a half in jail while authorities gather evidence against them.

Stern Hu, an Australian citizen, and his three Chinese co-workers who run Rio Tinto's Shanghai office, were detained on Sunday on charges of stealing top-secret information.

It emerged today that China's internal security agency is also claiming that, as well as spying, the four employees had bribed Chinese steel company workers during discussions over iron ore contracts.

The workers are accused of using "improper methods, roping in and bribing officials at Chinese steel producers” which “seriously damaged China's economic security and interests".

Rio and other iron ore suppliers are locked in discussions with China’s steel mills about iron ore pricing for 2009-10. These issues have not been resolved even though many contracts expired on June 30. Rio Tinto has refused Chinese demands for a bigger price cut.

The four Rio Tinto workers have not yet been officially arrested.

Approval to arrest a foreign national must be gained from the provincial level of the Public Security Bureau (PSB), China's criminal investigative body.

If arrested, defendants can be held for up to 10 months as the PSB gathers evidence.

Zhang Zaiping, a partner specialising in criminal law at Lusheng Lawyers, said: "In this period it's hard even for a defendant's lawyers to discover the charges against their clients," Mr Zhang said.

The Bureau must then present its evidence to a prosecutor — a process that can take up to five months. If the case reaches court, the hearing could last up to seven months.

The four Rio Tinto workers are facing life imprisonment for espionage. Australian consular officials are due to visit Mr Hu in detention later today.

Stephen Smith, Australia's Foreign Minister, said today: "China has its own laws about state secrets, they are clearly broader than the view that Australia might take.

"Frankly, it is difficult for a nation like Australia to see a relationship between espionage and national security and what appeared to be suggestions about commercial or economic negotiations."

"Having said that," Mr Smith continued, "Mr Hu now ... runs the risk of being subject to Chinese criminal, legal and judicial processes.''

Chinese officials in Canberra reassured Mr Smith's office that Mr Hu is being treated well and in accordance with Chinese law.

A spokesman for Rio Tinto said: "Rio Tinto is following developments very closely. The company is surprised and concerned by the allegations. We are not aware of any evidence that would support them. Rio Tinto is committed to high standards in business integrity and takes its ethical responsibilities very seriously.

"Rio Tinto has not been informed by the Chinese authorities of any charges in relation to these allegations. We remain ready to assist these authorities in their investigations. We will continue to contribute to work to support our employees and their families in China. In this regard we are liaising very closely with the Australian government."

Chinalco, China's state-owned metals giant, said in a statement on Friday that the detention of the Rio Tinto employees was not related to its failed bid earlier this year to invest $19.5 billion (£12 billion) in the Anglo Australian business.

Rio Tinto abandoned the deal under pressure from shareholders, opting instead to form a joint venture with BHP Billiton, its long-term rival, and a $15 billion rights issue.

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