"The company has disclosed to relevant authorities evidence that it has uncovered regarding possible violations of applicable anti-corruption laws involving interactions with government officials," BHP said.

'Internal investigation'

"Accordingly, the company is cooperating with the relevant authorities including conducting an internal investigation, which is continuing."

BHP is looking to combine its Australian iron ore operations with rival Rio Tinto [EPA]

It added: "It is not possible at this time to predict the scope or duration of the investigation or its likely outcome."

The statement was contained in BHP's quarterly report on production and exploration activities.

The company said it had responded to requests for information on the case from the US markets watchdog, the Securities and Exchange Commission.

The revelation comes as BHP seeks regulatory approval to combine its main iron ore operations in West Australia in a $116bn joint venture with Rio Tinto.

Steelmakers in Asia and Europe have urged regulators to block the venture, saying it would give Rio and BHP undue influence on the price of iron ore.

The price of ore has more than doubled on the spot market over the past 12 months amid a commodities boom fuelled by Chinese demand.

BHP and Rio are the world's third- and second-largest producers of iron ore, respectively.