A journal issued by China's state secrets watchdog has accused the mining multinational Rio Tinto of commercial spying over six years, saying data found on Rio computers showed the espionage had come at a huge cost to China.

Rio has said four employees detained in China, accused of espionage, did nothing unethical and has denied they bribed Chinese steel mills for information.

The report issued by China's National Administration for the Protection of State Secrets, however, 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 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, which appeared on an official website (www.baomi.org) of the secrets administration on Saturday.

The report also claimed 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 that estimate.

($1=6.831 yuan)

(Reporting by Chris Buckley; Editing by Nick Macfie)