(Reuters) - An investigative panel has found Japan's disgraced Olympus Corp hid up to $1.67 billion in losses from its investors, but stops short of recommending criminal charges against executives involved in the cover-up, a source said on Monday.

Separately, the Nikkei newspaper said that the panel was likely to state it had found no proof that the funds flowed to organized crime syndicates, as part of its report into the scandal engulfing the once-proud maker of cameras and medical equipment.

The panel's report is due to be released as soon as Tuesday, almost two months after Olympus's sacked chief executive, Englishman Michael Woodford, went public with his concerns over the firm's accounting for a string of murky acquisitions.

Olympus, which set up the panel, has since lost more than half its market value and risks being delisted from the Tokyo stock exchange, a humiliation that would cut it off from equity markets and put it under pressure to sell core assets.

The source familiar with the panel investigation said it found that former executive vice president Hisashi Mori and ex-internal auditor Hideo Yamada had led the cover-up of losses, which amounted to 130 billion yen ($1.67 billion) at its peak.

The panel has found Mori and Yamada then informed former president Tsuyoshi Kikukawa, the source added. Kikukawa at first publicly rejected the accusations of a cover-up when the scandal broke in October, but he later quit and the company conceded it had hid investment losses for as long as two decades.

The panel has not made any recommendations on the question of criminal complaints, arguing that this is outside its remit to get to the facts behind the cover-up, the source said.

That is up to the company, he said.

He could also not confirm a Nikkei report that the panel had also failed to find any proof of a link to organized crime.

Olympus is still under joint investigation by Tokyo police, prosecutors and the Securities and Exchange Surveillance Commission. The official investigations include a police unit dedicated to fighting organized crime or yakuza gangsters.