The US Justice Department told Fairfax, in response to a freedom of information request, it was conducting "law enforcement proceedings" involving BHP, which supplied the materials for gold, silver and bronze medals used in Beijing. The Department of Justice declined to comment after office hours on Tuesday.
Australian police confirmed they had been working with foreign counterparts and local regulators on Australian aspects of the US investigation.
BHP said it had been cooperating with "relevant authorities", and in response to media queries said it believed it had complied with all applicable laws in regards the sponsorship.
"BHP Billiton is fully committed to operating with integrity and the Group's policies specifically prohibit engaging in bribery in all its forms," BHP said in an emailed statement.