Nigerian authorities have seen documents suggesting the proceeds from past crude oil sales were diverted to personal accounts rather than reaching government coffers, President Muhammadu Buhari said on Wednesday, according to Reuters. Buhari, who took office in May after being elected on an anti-corruption ticket, said funds were "looted illegally". He could not provide more details, since various cases were being taken to court, he told journalists in a televised interview. Nigeria's former oil minister Diezani Alison-Madueke is under investigation as part of a crackdown on corruption in the oil industry. She has denied any wrongdoing. Buhari's latest comments suggested other officials might also be named.