More than 300 banks could fail in the US within three years, a gloomy new assessment warns.

RBC Capital Markets analyst Gerard Cassidy has doubled his estimate of failures from the 150 he predicted in February. Cassidy said the probability of failure is "very high" if a bank's nonperforming assets exceed the sum of tangible equity plus reserves for loan losses.

The Federal Deposit Insurance Corp (FDIC) took control of mortgage lender IndyMac last week after a Northern Rock-style bank run in which panicked customers withdrew more than $1.3 billion (£657 million) of deposits.

The FDIC has more than 90 lenders with $26.3 billion of assets on its " problem list". This excludes IndyMac, which had about $32 billion of assets, and almost $19 billion of deposits.

"You have to look at companies with the greatest exposure to the highest-risk assets, which include construction loans and exotic mortgages," Cassidy said.

"The final nail in the coffin for any depository institution would be a funding crisis where it is unable to gather deposits at reasonable cost, or wholesale funding markets are cut off."

The head of the FDIC yesterday moved to calm concerns that IndyMac depositors would be left short.

"All bank depositors should understand that their insured deposits are safe," chairman Sheila Bair said. "The chance that your own bank will be taken over by the FDIC is extremely remote. And if that does happen, you will continue to have virtually uninterrupted access to your insured deposits."

"No bank depositor has ever lost a penny of insured deposits," she added. "The overwhelming majority of banks in this country are safe and sound."

IndyMac specialised in mortgages that did not require borrowers to document income or assets. It was founded in 1985 by Angelo Mozilo and David Loeb, who also founded Countrywide Financial, which was taken over by Bank of America after being hit badly by the mortgage crisis.