SAO PAULO/MEXICO CITY, June 13 (Reuters) - Top management at bankrupt Brazilian retailer Americanas (AMER3.SA) slammed former executives, banks, and audit firms on Tuesday after a report by the company's legal advisers alleged their involvement in "fraudulently altered" financial statements.

Later in the day, Americanas' current top executive Leonardo Coelho assured lawmakers that board members were not among at least 30 people within the company he said were implicated in the financial scheme allegedly designed to hide its deteriorating balance sheet.

Americanas filed for bankruptcy protection in January after uncovering a $4 billion accounting scandal. The company accused ex-chief executive Miguel Gutierrez and half a dozen other former executives and employees of taking part in "fraud."

Gutierrez did not immediately respond to a request for comment, nor did other former executives named by Americanas or their lawyers.

The report was based on documents provided by an independent committee, the company said. It identified irregularities in cooperative advertising budget agreements, according to a securities filing.

It also found that the firm entered into a series of financing deals without proper corporate approvals.

"The improper accounting of these financing operations in Americanas' financial statements did not allow for the true determination of the company's indebtedness level," the filing said.

Accounting adjustments will be reflected in future financial statements as soon as auditing work is concluded, the company said, adding that the effects were still being ascertained.

"The management expects the impact on the most recent results to be significant," the company said, promising to evaluate ways it might be reimbursed for the damages.

CEO Coelho testified to a congressional committee that the report documents the fraud, and that purchase financing operations known as forfeit debts were not seen by any board members.

Coelho noted that firings of those involved started on Monday and were continuing on Tuesday.

He added that audit firms KPMG and PwC in Brazil allowed the amendment of letters on the request of the company's management, in order to eliminate inconsistencies in financial statements.

KPMG and PwC said they were unable to comment on client issues because of confidentiality clauses and professional secrecy rules.

Brazilian banks Itau Unibanco (ITUB4.SA) and Santander Brasil (SANB3.SA) were also mentioned in the investigation.

Coelho said that there was an "exchange of information" between banks and people inside the company in order to alter the words in documents exchanged between them regarding the financing processes.

Itau said in a statement that it acted with transparency and that financial statements were the responsibility solely of the company, and that it was "frivolous" to attribute responsibility for the fraud to third parties.

Santander Brasil said in a statement that Americana's securities filing proved "emphatically" the sole and exclusive responsibility of Americanas for accounting inconsistencies.

The documents exchanged between the bank and people inside the company were just "one among many sources of auditing" and Santander Brazil always fully reported all of the balances of Americanas' operations in the central bank system, the bank added.

Reporting by Gabriel Araujo, Andre Romani and Carolina Pulice; Additional reporting by Patricia Vilas Boas and Rodrigo Viga Gaier; Editing by Steven Grattan, Angus MacSwan, David Gregorio and Jamie Freed

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