Spokesmen for the British parts of the two accountancy firms stressed that the legal action, taken by the liquidators Price Waterhouse, would be confined to Singapore and have no impact in the UK.
A spokesman for Rajah and Tann, solicitors for Price Waterhouse, said: "The claim is in excess of S$1bn (each) for negligence in their audits of Barings Futures." Nick Leeson lost more than pounds 860m while in control of Barings Futures leading up to and after Christmas 1994.
The suit, filed in Singapore's High Court, also claims that the auditors failed to detect Leeson's hidden account 88888, which was used to hide the gigantic losses that brought down Britain's oldest merchant bank.
Deloitte & Touche is being sued for negligence for the period 1992-1993 and Coopers & Lybrand for the period from then leading up to the firm's collapse in February 1995.
Entirely separately, the UK administrators of Barings, Ernst & Young, are suing Coopers in the UK and both firms in Singapore. Ernst & Young have refused to discuss how much its own claims are for.
In Singapore, Deloitte & Touche's managing partner, Po'ad Mattar, confirmed the firm had been served a writ of summons and statement of claim by Price Waterhouse.
He said the suit was "not unexpected" but his firm was "disappointed" that the liquidators chose to sue them in Singapore.
Mr Mattar said Deloitte & Touche, which served as Barings Futures' auditors from 1986, when Barings Futures was incorporated, until 1993, was "completely satisfied that the audits ... were conducted with all professional skill and care."
David Compton, partner in Coopers & Lybrand, said the firm was not responsible for the collapse, saying investigations by both the Bank of England and the Singapore authorities had separately concluded that fraud and management failure were to blame.
"We are confident that our work as external auditors was properly carried out and we intend to vigorously defend any claims against us," he said. He said the firm was being sued for an audit it had not completed and would fight the claim.
The Singapore report by inspectors appointed by the Minister for Finance concluded that the bank collapsed because of "institutional incompetence" by senior management and a cover-up of escalating losses.
However, the report also questioned the audits by the two firms, saying they didn't follow appropriate steps to confirm account balances.
The inspectors criticised Deloitte's treatment of the key 88888 account, saying that while the auditors were aware it existed they did not do enough to check on how it had been used. Deloitte has used "inadequate procedures," they concluded.
Coopers & Lybrand Singapore replaced Deloitte as Barings Futures' auditors for the year ended 31 December 1994. The inspectors criticised Coopers, saying appropriate procedures "were not followed," "sufficient work was not done" and unusual transactions "were not adequately examined".