Sept 5 (Reuters) - Former Americanas Chief Executive Miguel Gutierrez denies any knowledge of accounting irregularities during the two decades he was at the helm of the Brazilian retailer, he said in a letter sent to congressional investigators

Gutierrez never "participated, authorized, ordered, tolerated or became aware of any act tending to manipulate the company's accounting or to enable any type of fraud", he said in the Sept. 4 letter sent to the congressional committee investigating the company's near-collapse and viewed by Reuters.

Americanas disputed Gutierrez's assertion, reiterating in a statement that independent advisers it had hired had found that management at the time had "fraudulently altered" documents to hide the circumstances that led to its bankruptcy filing.

The company, which runs of chain of stores and one of Brazil's largest e-commerce retailers, was thrown into crisis early this year by the disclosure of more than 20 billion reais ($4 billion) of accounting inconsistencies.

Allegations that Gutierrez and other executives were involved in accounting fraud were first made in June.

The letter marks the first time that Gutierrez has addressed the allegations.

Several former Americanas directors have testified before the congressional committee in the past few weeks. Gutierrez has been invited to testify but has said that health issues have prevented him from doing so.

In the letter, Gutierrez also said that reference shareholders in Americanas - Brazilian billionaires Jorge Paulo Lemann, Carlos Alberto Sicupira and Marcel Telles - and board members "had responsibilities relating to the financial and accounting issues of the company".

On Tuesday the trio's holding company, LTS, also rejected Gutierrez's accusations.

LTS said his comments "do not provide any proof of his allegations or refute evidence of his participation in the fraud". The holding company described what happened at Americanas as "cunning fraud".

Gutierrez's immediate successor, Sergio Rial, said in testimony last week that he had not seen any evidence that the reference shareholders or board members had participated in the fraud. ($1 = 4.9373 reais) (Reporting by Carolina Pulice Editing by Edwina Gibbs and David Goodman)