The Central Bank has written to the Government on the scope of its regulatory duties in the aftermath of the Allfirst fraud, which cost AIB $691 million (€712 million).

The Department of Finance confirmed receipt of a letter from the Bank's governor, Mr John Hurley, which was sent on Tuesday.

Neither the Bank nor the Department would discuss the contents of the letter, which is likely to cite the functions of the new Irish Financial Services Regulatory Authority.

The Bank is known to have been "seriously concerned" about the fraud and has sought urgent independent reviews of the risk- control systems at every financial institution in the State.

It told banks and building societies that the Allfirst affair had highlighted the need for strong systems of internal control and risk management. The Central Bank also sought "independent verification" that the system in each organisation was sound.

The letter was requested by Mr McCreevy when AIB disclosed in February that its US subsidiary Allfirst had been hit by fraud. The bank blamed rogue trader Mr John Rusnak, who has since been charged with fraud in the US. He has pleaded not guilty.

Mr McCreevy said in February that there "may be lessons for legislators" in the fraud.

He said: "I have asked the Central Bank to report to me, in the light of these events and of their own investigations thereof, as to whether any changes to the legislative provisions governing banking supervision might be required."

The Central Bank did not sanction AIB after its own investigation into the fraud.

An AIB report, produced by former US banker Mr Eugene Ludwig, outlined a litany of bullying, laziness and weak management that led to the fraud going undetected until it was in its sixth year.

The Central Bank gave banks until the end of July to show that they were not vulnerable to the same sort of fraud.