Oil majors Shell and Eni have denied reports that they knew money paid to the Nigerian government for a valuable oil field would be passed to a convicted money launderer and used to pay political bribes.
The firms have denied any wrongdoing by their employees after reports that internal emails showed they knew the $1.3bn (£1bn) paid for oil block OPL 245 in 2011 would go to ex-Nigerian oil minister Dan Etete and that they were negotiating with Etete for a year before the deal was finalised.
OPL 245 is an oilfield off the coast of Nigeria which holds an estimated nine billion barrels of oil, worth nearly half a trillion dollars at today's prices.
Courts in Nigeria and Milan are investigating the 2011 purchase of the block.
A spokesperson for Shell said: "Given this matter is currently under investigation, it would be inappropriate to comment on specifics. However, based on our review of the Prosecutor of Milan's file and all of the information and facts available to Shell, we do not believe that there is a basis to prosecute Shell. Furthermore, we are not aware of any evidence to support a case against any former or current Shell employee.
"If the evidence ultimately proves that improper payments were made by Malabu or others to then current government officials in exchange for improper conduct relating to the 2011 settlement of the long-standing legal disputes, it is Shell’s position that none of those payments were made with its knowledge, authorization or on its behalf."
Itlay's Eni told Reuters the allegations made were not supported by the facts, the underlying agreements or the independent investigations concluded to date.