Six employees of Wall Street retail brokerage Sky Capital Holdings Ltd surrendered to the FBI on Wednesday on charges of a $140 million investment fraud and stock manipulation in the United States and Britain, officials said.

The firm's founder, President and Chief Executive Officer Ross Mandell and five others were charged in a criminal indictment announced by U.S. prosecutors and parallel civil case by the U.S. Securities and Exchange Commission.

The six were charged in a two-count indictment to commit securities, wire and mail fraud for a purported scheme to defraud investors between 1998 and 2006.

Calls to phone numbers listed for the New York brokerage went unanswered or were busy.

A published overview of the company said that Sky Capital Holdings, through subsidiaries such as Sky Capital LLC, provided financial services and products for international clients. It has another subsidiary Sky Capital UK Ltd.

Until late 2006, Sky Capital's shares were traded on the Alternative Investment Market of the London Stock Exchange.

"Investor funds were substantially used to enrich the defendants and others; to pay excessive undisclosed commissions to brokers and to pay off victims who had lost money through prior purported investment opportunities," the Office of the U.S. Attorney in Manhattan said in a statement.

Apart from Mandell, other principals and employees Stephen Shea, Adam Harrington, Arn Wilson, Robert Grabowski and Michael Passaro surrendered to the FBI on Wednesday morning, FBI spokesman Jim Margolin said.

They were expected to appear in Manhattan federal court later in the day.