China's state secrets watchdog has accused mining multinational Rio Tinto of engaging in commercial spying over six years, saying data on Rio computers showed the espionage came at a huge loss to China.

The report and other comments from the secrets agency also said the case of four Rio four employees detained and accused of espionage, including one Australian, could foreshadow stricter controls on how foreign companies do business in China.

Rio has said its employees did nothing unethical and did not bribe Chinese steel mills for information.

The report issued by China's National Administration for the Protection of State Secrets said Rio Tinto's commercial spying involved winning over and buying off, prying out intelligence, routing one by one, and gaining things by deceit over six years.

The large amount of intelligence and data from our country's steel sector found on Rio Tinto's computers and the massive damage to our national economic security and interests are plainly obvious, said the Chinese-language report issued on a website (www.baomi.org) of the secrets administration on Saturday.

China has detained the Rio workers -- Australian Stern Hu and three Chinese colleagues -- on allegations of stealing state secrets about iron ore price negotiations.

The detentions have raised worries about doing business in China, strained ties with Australia and overshadowed the critical 2009 iron ore price talks. Rio's share price, however, has been little affected.

The new Chinese report said Rio's spying meant Chinese steel makers paid over 700 billion yuan ($102 billion) more for imported iron ore than they otherwise would have. It did not explain how it arrived at this estimate.

A Rio spokeswoman in Australia said on Sunday she was unaware of the Chinese report and declined to comment further.

The report from the secrets watchdog suggests the Chinese government is unlikely to drop the Rio case and could instead use it as a springboard for tougher information controls on domestic and foreign businesses.

It said the case should force Chinese officials and companies to do more to protect sensitive commercial information, and foreign businesses in China must come under stricter controls to deter them from spying.

Our country has entered a peak period of commercial espionage warfare, and the threat to important economic intelligence and security of national economic activity increases by the day, the report said.

The report and others on the state secrets website said the government should spell out more clearly what commercial data count as official secrets.

Contacts between local officials, experts and managers and foreign businesses should also be more strictly controlled, said the report on Rio, adding that traitors were enriching themselves at the expense of Chinese businesses.

The Rio Tinto spying case has again sounded the alarm over secrets protection by our country's state-owned enterprises and corporations, wrote Luo Jianghuai, a secrets protection official in eastern Jiangsu province, an essay accompanying the report on Rio.

Luo said multi-nationals used Chinese staff with experience in local businesses and government to illicitly gain information and influence.

Luo's essay and the report on Rio appeared in the August issue of the secrets watchdog's official magazine, Secret Protection Work, according to the website.

(Additional reporting by Chris McCall in Sydney; Editing by Nick Macfie)

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