ExxonMobil and other leading oil companies are to face an investigation into how up to $500m (£310m) came to be paid into a private US bank account, said to be solely controlled by the President of Equatorial Guinea. Global Witness, a London-based anti-corruption campaign group, has written to John Ashcroft, the US Attorney General, asking him to look into allegations that Equatorial Guinea's ruler, Teodoro Obiang Nguema Mbasogo, has between $300m and $500m deposited in the Dupont Circle branch of Riggs Bank in Washington, DC.