Media reports say the Federal Bureau of Investigation (FBI) inquiry involves the bank’s practice of giving home loans to risky borrowers.

The FBI would not name IndyMac, but said it had widened its investigation of the US sub-prime mortgage industry to 21 firms, up from 19.

IndyMac was seized by US regulators amid fears it was running out of cash.

The bank said it did not know anything about the investigation prior to reading about it in various media reports.

“We’re not in a position to confirm or deny (the investigation) because it’s an uncorroborated press account,” said an IndyMac spokesperson.

He added: “It shouldn’t be surprising that there is an investigation because of the size of the bank failure.”