ABUJA - Nigeria's former attorney general was detained by the country's financial crimes agency upon his return home on Thursday, the commission said in a statement, as part of an investigation into one of the oil industry's biggest suspected corruption scandals.

Mohammed Adoke was arrested by Interpol in November after travelling to Dubai for a medical appointment. He voluntarily flew back to the West African country on Thursday, his lawyer said.

The Economic and Financial Crimes Commission (EFCC) investigation relates to the $1.3-billion sale of a Nigerian offshore oilfield known as OPL 245 by Malabu Oil and Gas in 2011.

Eni SpA and Royal Dutch Shell jointly acquired the field from Malabu, which was owned by former Petroleum Minister Dan Etete.

The sale of the oil field has spawned legal cases across several countries, involving Nigerian government officials and senior executives from Eni and Royal Dutch Shell.

Shell and Eni, and their executives, have denied any wrongdoing. Etete has also denied wrongdoing.

"His return to Nigeria clears the way for him to answer to the charges against him," the EFCC said in a statement, following Adoke's return to Nigeria.

Adoke's lawyer, Mike Ozekhome, said the former attorney general was released by Interpol and Dubai authorities after "finding nothing criminal against him."

"Our client remains very confident that he will be vindicated in the court of law and justice at the end of the day, after a free and fair trial," Ozekhome said in a written statement.

Adoke served as attorney general from 2010 to 2015.

Ozekhome previously said his client had appeared in court in Nigeria in the past over the OPL 245 case and was exonerated.