The 6.8 percent tumble in Olympus' stock also followed a surprise lawsuit by medical equipment maker Terumo Corp, which is vying with Sony Corp, FujiFilm Holdings and other companies to inject money into the cash-strapped company in return for a stake.

Olympus in October told the U.S. Department of Justice about travel, meal and entertainment expenses paid by its U.S. subsidiary to doctors in a training program in Brazil that may have violated the Foreign Corrupt Practices Act, company spokesman Osamu Kobayashi said on Wednesday, confirming an earlier Bloomberg report.

Bloomberg on Wednesday quoted Chairman Yasuyuki Kimoto as saying in a July 23 interview, "We understand DOJ is trying to gather lots of information on us."

"Olympus might have to be investigated further because of this," said Nanako Imazu, an analyst at CLSA Asia-Pacific Markets in Tokyo. That whiff of fresh trouble is a concern for jittery Olympus investors, she noted.

Kimoto also told Bloomberg that the enquiries into Olympus' U.S. unit may be part of a wider industry probe.

STRONG-ARM TACTICS?

The decision by Terumo to seeks damages for loss of shareholder value from the accounting fraud that rocked Olympus last year might be a tactic by Japan's leading maker of catheters and artificial hearts to garner more attention for its tie-up proposal, one corporate governance expert said.

Olympus said in a statement on Wednesday it had received a claim for 6.6 billion yen ($84 million) in damages from Terumo.

Terumo, which has proposed investing some $640 million in Olympus, is suing Olympus under Japan's Financial Instruments and Exchange Act for failing to disclose its accounting fraud before signing a business and capital tie-up with the medical equipment firm seven years ago.

"This sounds to me like a sharp wake-up call to Olympus, to bring them to the negotiating table," said Nicholas Benes, a corporate governance expert who runs the Board of Director Training Institute of Japan.

In a bid to underpin its finances, Olympus is considering tie-up offers from at least four other domestic firms, including those from Sony and Fujifilm.

Terumo's lawsuit is the first made by an institutional shareholder against the firm, which admitted last year it had used improper accounting to conceal huge investment losses under a scheme that began in the 1990s.

"Olympus will very much not want a significant shareholder suing it based on the securities laws, as that could provoke other shareholders to sue," said Benes.

The endoscope maker said in its statement it didn't expect other shareholders to file similar lawsuits.

Shares in Olympus have fallen 44 percent since last October, when the company's former CEO Michael Woodford blew the whistle on the decade-long accounting fraud at the firm.

The risk for the winner of the battle to woo Olympus is that it overpays for a stake in a company that may not have finished revealing past problems, said Yasuo Sakuma, portfolio manager at Bayview Asset Management.

"There's probably a lot more skeletons in its closet to come out. This Brazil case is one of them," Sakuma said. ($1 = 78.1000 Japanese yen)

(Reporting by Tim Kelly, Linda Sieg, Reiji Murai, Sophie Knight, Junko Fujita and Dominic Lau; Editing by Edwina Gibbs, Chris Gallagher and Ryan Woo)

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