TOKYO (Reuters) - Japanese police have arrested four men on suspicion of defrauding U.S. investment bank Lehman Brothers LEH.N by using fake documents carrying trading firm Marubeni Corp's (8002.T: Quote, Profile, Research) letterhead, a police spokesman said.

The four are suspected of forging the documents to obtain over 9 billion yen ($83 million) in funds from the bank last October, the Tokyo Metropolitan Police said on Monday.

The arrests come after Lehman on March 31 filed a lawsuit against Marubeni to recoup some $352 million, blaming Marubeni staff for the swindle.

It seeks to recover loans made last year to finance a revamp of hospitals and lease medical equipment via Asclepius, a now bankrupt unit of drug firm LTT Bio-Pharma Co (4566.T: Quote, Profile, Research), and arranged through Marubeni staff, a source with direct knowledge of the matter said in March.

Marubeni, Japan's fifth-biggest trading house, restated in a statement on Monday that it was not involved in the scam and had no obligation to pay Lehman.

The trading firm said it had fired on March 10 Shingo Yamaura, a former part-time worker at Marubeni.

The Tokyo Metropolitan Police said the four arrested were Yamaura, 35; Shigenori Saito, 46, former president of Asclepius; Yuzuru Yamanaka, 34, former president of LTT Bio-Pharma; and Fumihiro Takahashi, 61, president of a Tokyo-based building planning company,

A spokesman for Lehman Brothers in Tokyo said the company had no comment on the arrests.

In the scam, investors such as Lehman paid around 108 billion yen between May 2006 and November 2007 in loans for what they were told were hospital revamp projects, the Nikkei business daily and other media outlets reported on Monday.