The UK Serious Fraud Office has joined a global investigation into Rio Tinto's dealings in the West African nation of Guinea.
The SFO confirmed it has opened an investigation into "suspected corruption in the conduct of business in the Republic of Guinea by the Rio Tinto group, its employees and others associated with it".
The investigation follows Rio Tinto's self-reported concerns over a $US10.5 million ($13 million) payment made to a consultant negotiating with Guinea's President Alpha Conde on the giant Simandou iron ore project in 2011.
The SFO joins the US Department of Justice and the Australian Federal Police in investigating the events surrounding the awarding of mining rights to the $US20 billion project.
The Simandou project was once touted as one of Rio's major growth opportunities, but instead turned out to be a frustrating drain on resources and now a global embarrassment.
Having failed to get the $US13 billion needed to fund its share of the mine's development, Rio late last year announced it would sell its 47 per cent stake in the project to its Chinese state-owned partner, Chinalco, for around $US1.2 billion.
In the wake of the investigations, one senior Rio executive has been suspended, while another left the company prematurely and former chief executive Sam Walsh had a portion of his retirement payouts delayed pending the outcome.
Rio's share price opened lower, down 0.2 per cent to $62.47 per share at 11:00am (AEST).
