The top lawyer for UBS's investment banking unit is reportedly at the centre of a civil probe by New York's attorney-general into an alleged fraud in which the bank is said to have dumped worthless securities on investors as the subprime crisis grew.

General counsel David Aufhauser is the person described in New York attorney Andrew Cuomo's case against UBS as "Executive A", according to the Wall Street Journal.

Aufhauser has not been named by Cuomo and has not been charged with any wrongdoing. None of the parties would comment.

He was formerly the general counsel to the US Treasury Department.

Last week, Cuomo sued UBS, accusing it of committing a "multi-billion dollar fraud" by steering clients into auctionrate securities that became impossible to sell once the credit market tightened. the legal action by Cuomo said at least seven UBs executives dumped $21 million (£10.6 million) in auction-rate securities held in personal accounts as the credit market began showing signs of trouble, and that the bank continued to sell those securities.

UBS has said it conducted an internal probe of alleged sales of personal holdings of auction-rate debt by its executives and found no wrongdoing.

Victims of the alleged fraud included tens of thousands of individual investors along with 250 companies, Cuomo says.

"Top executives jumped ship as soon as the securities market started to collapse, leaving thousands of customers holding the bag," he says.

UBS denies the claims and says it will defend itself "vigorously".