AIB borrowed tens of billions of dollars in emergency loans from the US Federal Reserve over a period of a year to supplement the funding it was getting from the European Central Bank.

AIB used its office in New York to get access to the US-government-backed money starting in early 2009. The move came as a result of the capital markets losing confidence in Irish banks which severely curtailed their funding.

The bank took short-term loans ranging in size from $300m to $4bn at regular intervals, pledging its US loan book as collateral.

The loans had terms of 28 days or 84 days and were rolled over frequently, but the amounts borrowed increased with time.

The extent and amount of borrowing shows how precarious AIB's funding situation was from early 2009, when the Irish government recapitalised the bank with €3.5bn, right through this year.

The Federal Reserve made the cash available under its term auction facility, a $3.3bn programme to supply desperately needed liquidity to American banks which went into operation in 2007.

It emerged last week that the Fed had been lending significant sums of money to banks outside the US, as well as corporations inside the country, such as General Electric and McDonald's and investors like Pacific Investment Management.

The revelation that the government had been quietly helping foreign institutions has proved very controversial in the US.