* Shell says ex-executive may have committed a crime
* Complaint relates to sale of Nigeria oilfield
* Says new evidence unrelated to Italy court case
* Evidence of possible kickbacks to Seychelles company - source (Adds statement from Neconde Energy)
By Ron Bousso and Libby George
LONDON, March 28 (Reuters) - Royal Dutch Shell has filed a criminal complaint against a former senior employee over suspected bribes in the $390 million sale of an oilfield in Nigeria, where the company is already under investigation over a separate deal.
Dutch prosecutors confirmed they had received the complaint against Peter Robinson, a former vice president for sub-Saharan Africa. They said it would be included in an ongoing investigation into Shell and Italy's Eni over the acquisition of a different Nigerian oilfield, known as OPL 245.
Shell and Eni deny any wrongdoing related to OPL 245, in which Robinson is being prosecuted. A spokesman for Anglo-Dutch Shell said the two cases were unrelated.
Chiara Padovani, a lawyer representing Robinson, said in a statement he denied any allegations of misconduct. Robinson has not been contacted by Dutch authorities about any such complaint, she added.
"Our client regrets that an issue between him and his former employer has been drawn into the public domain. He has not been informed of the details of Shell's complaint against him," Padovani said.
Shell said an internal investigation had found that Robinson may have committed a crime during the sale of an onshore oilfield, Oil Mining Lease (OML) 42, to local company Neconde Energy Ltd in February 2011.
"We suspect a crime may have been committed by our former employee, Peter Robinson, against Shell in relation to the sale process for Oil Mining Lease (OML) 42 in Nigeria in 2011," a Shell spokesman said in a statement.
"We have filed a criminal complaint with the Dutch authorities and are considering other steps we could take."
In a statement, Neconde Energy said it purchased its stake in the field following a competitive bidding round and made no payments to Robinson, Shell or other companies in order to facilitate it.
"Neconde completely denies any allegation or suspicion of kickback for the acquisition of its interest in OML 42 and the statement credited to Shell suggesting the contrary is untrue and most unfortunate," the company said.
Robinson is one of a number of Shell employees being prosecuted in Milan over OPL 245, a case spanning several countries that involves Nigerian government officials and oil executives in a $1.3 billion sale of the offshore field.
The new evidence was uncovered after investigators looking into OPL 245 raided a house in Perth, Australia owned by Robinson, according to a source close to the process.
The evidence included documents showing Robinson had set up a Seychelles-based company, which was later linked to two Swiss bank accounts set up in 2011 also under Robinson's name, the source said. Shell suspects that the company and the accounts may have been used to process kickbacks, the source said.
In court filings, the Milan prosecutor requested that Swiss authorities investigate and freeze two accounts opened at a Geneva bank in the name of Seychelles-based Energy Venture Partners Ltd to check their connection to Robinson.
Reuters was unable to contact Energy Venture Partners.
Shell, the largest international oil producer in Nigeria, was looking methodically at other transactions in which Robinson was involved, the source said.
The spokesman said Shell had informed the U.S. Department of Justice and the U.S. Securities and Exchange Commission about the offshore company and the accounts.
Swiss federal prosecutors have supplied information to authorities in Italy and the Netherlands probing alleged corruption related to oil contracts in Nigeria, the Office of the Attorney General said on Wednesday.
Additional reporting by Shadia Nasralla in London, Anthony Deutsch in Amsterdam, Emilio Parodi in Milan and Chijioke Ohuocha in Abuja. Editing by Dale Hudson and Adrian Croft