UPDATE 3-Shell targets former senior executive in Nigeria graft complaint

* Shell accuses ex-executive of 'crime' during oilfield sale

* Says new evidence unrelated to Italy court case

* Evidence of possible kickbacks to Seychelles company - source (Adds further Shell comment)

LONDON, March 28 (Reuters) - Royal Dutch Shell has filed a criminal complaint against a former senior employee over suspected bribes in the 2011 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 Anglo-Dutch 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. A Shell spokesman said the two cases were unrelated.

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."

Chiara Padovani, a lawyer representing Robinson, did not respond to a request for comment. Neconde Energy was not immediately available to comment.

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.

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.

(Additional reporting by Shadia Nasralla in London, Anthony Deutsch in Amsterdam, Editing by Dale Hudson)