Alistair Darling is not the first to call for credit agencies to be probed

Mr Darling called for "international action" to review the regulation of the agencies and banking systems.

The agencies have been criticised for giving upbeat assessments of investments which turned out to be linked to risky home loans in the US.

Because of heavy losses on these deals, there is less willingness to lend cash.

Mr Darling, who approved emergency Bank of England funding to Northern Rock on Thursday, said that a probe was warranted.

"International action is needed to ensure that in the future we can reduce the risk of this sort of turbulence occurring again," he said at a meeting of EU finance ministers in Porto, Portugal.

'Conflict of interest'

On Friday, the US Financial Services subcommittee on capital markets said that it would hold a hearing into the role of credit rating agencies in the structured finance market - including mortgage-backed securities.

And the EU Financial Services Commissioner, Charlie McCreevy has called on the EU and the US to join forces to investigate the role of credit rating agencies.

That rating agencies were rating investments without the ultimate investors knowing what was behind the bonds is a problem

Jean-Claude Trichet

President

European Central Bank

Earlier, president of the European Central Bank, Jean-Claude Trichet, said that lessons needed to be learned from the fact that the fees of the credit rating agencies were paid by the very financial institutions whose bonds they are assessing.

"The fact that conflict of interest might appear is something we must reflect upon, as is the fact that we have very few credit rating agencies at a global level," Mr Trichet said.

"And that rating agencies, in a number of cases, were rating investments without the ultimate investors knowing what was behind the bonds is a problem.

"The credit rating agencies knew, but it was considered confidential information."

German banks have been badly hit by the problems linked to the US sub-prime mortgage crisis, and Chancellor Angela Merkel has also been critical of the agencies for not alerting the markets to companies with problems amid the current market instability.

There has been criticism of the high ratings given to bundles of debt that included sub-prime mortgages, which are offered to homebuyers with inferior credit ratings.

Mortgage default rates have risen in the US as it emerged that many people had been given loans on which they were unable to meet repayments.