The Australian government had yet to be officially notified of the formal arrests, a foreign affairs department spokeswoman said on Wednesday.
Speedy resolution urged
The department was following the case "patiently" and urged Beijing to resolve the case "as soon as possible", she told the AFP news agency on Wednesday.
"We continue to pursue the matter actively in Canberra, Beijing and Shanghai," she added.
The detentions have sparked a diplomatic row between the two countries that conducted $57bn worth of trade last year, with Beijing earlier telling Canberra not to interfere after Kevin Rudd, Australia's prime minister, warned its economic interests were at stake.
|China has been pressing for price cuts to iron ore to fuel its rapid industrialisation [AFP]
Hu was detained with three Chinese colleagues in Shanghai on July 5 while Rio Tinto was acting as lead negotiator for global iron ore suppliers in price talks with Chinese steel mills.
China's steel industry consumes up to 60 per cent of global iron ore production and Beijing has been pressing for deep price cuts after two years of increases totalling more than 120 per cent.
Chinese officials had previously suggested the men may be charged with stealing state secrets, but there was no mention of the more serious crime in Xinhua's report on Tuesday.
Rio Tinto, which has been keeping mostly quiet about the case in public, had no immediate response to the report, but said earlier on Tuesday that it "still not aware of any evidence that would support their detention".
In a statement last month, Rio said it believed allegations of bribery against the workers were "wholly without foundation".
Last week, Liu Jieyu, the Chinese vice-foreign minister, on a visit to Australia, urged Canberra to respect his country's legal system and not interfere with the case against Hu.