Nemazee was a national finance chair of U.S. Secretary of State Hillary Clinton's 2008 presidential campaign, and a supporter of John Kerry's run for the White House in 2004.

He typically donates more than $100,000 annually to Democratic political candidates, including Senate Majority Leader Harry Reid and Senator Charles Schumer, and sits on the board of the Iranian American Political Action Committee.

Bill Clinton, when he was president, nominated Nemazee to be U.S. ambassador to Argentina.

Prosecutors said Nemazee, the chairman and chief executive of Nemazee Capital, sought to induce Citigroup's banking unit to lend up to $74 million based on fraudulent and forged documents suggesting that he had hundreds of millions of dollars of accounts available as collateral.

They said Nemazee also provided Citigroup with fake references so that when the bank would try to confirm details about his accounts, it would actually be contacting him. The scheme lasted from December 2006 to this month, the prosecutors said.

Prosecutors said federal agents stopped him Sunday at Newark Liberty International Airport as he prepared to board a flight to Rome, and that he repaid a more than $74 million loan to Citigroup the following day.

Nemazee has homes in Manhattan and the suburb of Katonah, New York, prosecutors said.

According to its Web site, Nemazee Capital is a private equity firm that was founded in 1987 and specializes in financial services. It said its acquisitions have included Carret Asset Management, a privately held firm founded by legendary investor Philip Carret, and part of what is now Brean Murray Carret & Co, a small investment bank.

Brean did not immediately return a request for a comment. Citigroup spokeswoman Shannon Bell said the bank is working with authorities on the matter.