Rio acquired Riversdale, the owner of Mozambique coal assets, in 2011 for around $A4 billion.

In January 2013, the company announced a $US3 billion impairment on the assets and the departure of Doug Ritchie, who lead the acquisition, as well as CEO Tom Albanese, who was replaced by Sam Walsh.

Rio said overnight that it was cooperating with inquiries from relevant authorities relating to the impairment in the 2012 accounts.

The company offloaded the assets in 2014.

“As the SEC investigation, which started in April 2013, remains ongoing it would be inappropriate to comment further at this time,” Rio said.

“The company will update the market, as required, in due course.”

The news comes weeks after Rio announced it was investigating a $10.5 million payment made to a consultant working on the Simandou iron ore project in Guinea.

So far that investigation has resulted in the termination of senior executives Alan Davies and Debra Valentine, but the internal probe is continuing.

Rio shares gained A95c yesterday to $58.70.