Rio Tinto confirmed this morning that it is the subject of a long-running US Securities and Exchange Commission (SEC) probe.
The investigation, which started in April 2013, relates to a $3bn (£2.4bn) impairment charge lodged in its 2012 accounts in respect of Rio Tinto Coal Mozambique.
Rio Tinto Coal Mozambique housed assets the company picked up when it took over Riversdale Mining in 2011 but it subsequently sold these in 2014.
The Anglo-Australian miner, which issued its statement in response to earlier press speculation, added that it was cooperating with the inquiries.
Shares in the FTSE 100 company are down 1.3 per cent at 2,952p at time of writing.
The SEC investigation is not the only hardship facing the company at the moment, as it struggles through challenging commodities markets. In its results for its first half of 2016, the firm revealed that its underlying earnings had nearly halved.
At the time the results were released, recently appointed chief executive Jean-Sebastien Jacques said he was keen to cut back costs at the firm, as he did not see the market conditions becoming less challenging any time soon.