"We've stressed the importance of getting further and better details," he said.

"We have no information as to what the investigation does involve. We're going on the basis of press reports. The government here is not able to inform us anymore.

'Different' rules

"We respect the Chinese legal system and the processes that need to be gone through, but we've indicated that this too is an important issue back home in Australia."

Crean said Australia is also pushing for the presence of legal representation for Hu as well.

"We have a different set of rules back home for the treatment of individuals than is the case here. ... We have to respect their system and work within it."

Australia's PM Rudd says the case requires careful handling [Reuters]
Chinese media on Friday said, citing a statement from the country's internal security agency, that the four Rio workers obtained confidential information including summaries of meetings by Chinese negotiators in the talks on annual iron ore supply contracts.

"This seriously damaged China's economic security and interests," the state-run China Securities Journal said, echoing a foreign ministry official statement a day earlier.

On Thursday Qin Gang, China's foreign ministry spokesman, said that Chinese authorities had "a vast amount of irrefutable evidence" which showed the four "stole Chinese state secrets for overseas, gravely harming China's economic interests and economic security".

Rio Tinto, based in London and Australia, is the world's third-largest mining company and the lead negotiator for global iron-ore suppliers in price talks with Chinese steel mills.

Threat to relations

The case threatens to cast a shadow over Australia's trading relations with China, one of Canberra's most important trading partners.

Australian opposition politicians have criticised the country's prime minister, Kevin Rudd, for not doing enough to intervene in the case.

But on Friday Rudd defended his actions, saying the issue required a careful approach so as not to trigger a trade crisis, accusing some politicians of "grandstanding" over the case for domestic political reasons.

"The business of dealing with difficult, complex diplomatic questions, particularly when human lives are concerned, requires sensitivity and proper handling," Rudd told Australia's ABC radio from Italy, where he was attending the G8 summit.

Iron ore price negotiations have already run past their original June 30 deadline and last month Rio Tinto ditched a planned $19.5bn investment by state-owned Chinese metals firm Chinalco.

The latter case has sparked speculation in Australia that the arrests may be in reprisal for the collapsed Chinalco deal.