PARIS (Bloomberg) - Willis Group Holdings Ltd., the world's third-largest insurance broker, was sued by clients of Stanford Financial Group over claims Willis aided an alleged $7 billion fraud by Stanford.

The complaint filed yesterday in federal court in Dallas by investors from Latin America seeks class-action status and claims Willis violated Texas securities laws by vouching for Stanford in letters he used to solicit customers.

Willis actions "crossed the line from the role of insurance brokers, to acting as sales agents for Stanford Financial", lawyers for the group said in an e-mailed statement on Friday.

Stanford Financial is one of three businesses led by R Allen Stanford that were sued by the US Securities and Exchange Commission for misleading investors. Stanford, 59, has been in custody since June 18, when he was arrested after a Houston grand jury indicted him for allegedly running a Ponzi scheme.

Willis Group declined to comment on the lawsuit, said Louise Brett, a spokeswoman for the insurer in London.