Ousted Nissan Motor Co. Chairman Carlos Ghosn admitted to prosecutors that he signed documents on his post-retirement pay that were unreported in the company's securities statements, sources close to the investigation said Thursday.

The act of signing, which Ghosn allegedly denied shortly after his arrest on Nov. 19, is seen by prosecutors as more proof that the former chairman of the Japanese automaker violated the financial exchange law by failing to report part of his remuneration.

But the sources said that the 64-year-old has argued that the signing of the papers was only to confirm his understanding of the documents' contents, apparently maintaining that he did not commit financial misconduct.