WASHINGTON (Reuters) - IndyMac IDMC.PK is under investigation by the FBI for possible fraud involving home loans made to risky borrowers, The Associated Press reported on Wednesday, citing an unnamed law enforcement official.

The report said it was not immediately clear how long the FBI's probe of the bank has been ongoing but the probe is focused on the company and not individuals who ran the thrift institution.

U.S. banking regulators seized mortgage lender IndyMac on Friday after withdrawals by panicked depositors led to the third largest banking failure in U.S. history.

The FBI declined to comment on IndyMac, but a spokesman earlier on Wednesday said the FBI's probe of corporate fraud in the subprime lending industry had risen to 21, from 19 in April. He provided no details.

"The FBI currently has 21 investigations related to the subprime market industry. We receive information from a variety of sources on a daily basis, and we have an obligation to review each allegation on its merits," spokesman Jason Pack said when asked about IndyMac.

"Given the volatility of today's subprime market, we have seen an increase in subprime related complaints. To protect the integrity of our cases, we do not confirm or comment about specific companies that may or may not be a part of our investigations," he said.

Bureau spokesman Richard Kolko, asked whether IndyMac was under investigation, noted the expansion of the industry probe but said he had no names.

The bureau has publicly acknowledged only one company -- Doral Financial Corp -- as involved in its corporate probe of the mortgage industry. The largest U.S. mortgage lender, Countrywide, also is under FBI investigation, authorities have said, although the FBI has declined to comment and Countrywide said it was unaware of any investigation.

When the FBI disclosed its industry investigation, major investment banks Goldman Sachs (GS.N: Quote, Profile, Research), Morgan Stanley (MS.N: Quote, Profile, Research) and Bear Stearns Cos each said the government had asked them for information, but there was no confirmation of any FBI role. Beazer Homes (BZH.N: Quote, Profile, Research) said last year it had received a federal grand jury subpoena related to its mortgage business.