The U.S. investment bank Lehman Brothers Holdings Inc. plans to file a lawsuit against the trading company Marubeni Corp. to recover hundreds of billions of yen it lost to alleged investment fraud, a company official said Sunday.

Lehman is seeking to recoup ¥35 billion it loaned to a fund run by a unit of Japanese biotechnology company LTT Bio-Pharma Co., a Lehman official said on condition of anonymity, citing the sensitivity of the case. The funds were secured by Marubeni.

A unit of LTT-Bio Pharma, a medical consulting company that acted as the fund organizer, filed for bankruptcy March 19, leaving investors stuck with massive outstanding loans that were misappropriated in the alleged fraud.

Lehman Brothers Japan Inc. plans to file a civil suit Monday at the Tokyo District Court to demand Marubeni pay back the loans it secured, the company official said.

Marubeni has denied any wrongdoing and has said it doesn't have to cover any damage from the fund because the deal involved fake documents. It fired two employees for allegedly collaborating with the fund organizer to forge documents and has filed a separate criminal complaint against the fund operator.

Lehman contends that in addition to securing the loans, Marubeni is responsible for repayment because meetings were held at the Marubeni office to discuss the fund before the agreement was struck late last year.

Officials of LTT-Bio-Pharma, its bankrupt unit and its lawyer were not available for comment Sunday.