A stock trader in Tennessee has pleaded guilty to defrauding investors in a $21 million  Ponzi scheme, and a Colorado man  is being accused of running a $12 million real estate Ponzi scheme in Denver, according to the Associated Press.

Dennis Bolze, pleaded guilty on Tuesday  to wire fraud and money laundering charges in US District Court  in Tennessee and faces up to 90 years in prison if the maximum terms are applied when he is sentenced 15 April.

Under the guise of a legitimate stock trading operation, Mr Bolze was accused of  running a scam between 2002 and 2008 in which initial investors were paid with money put in by subsequent investors.

Up to 100 people in 12 countries were defrauded, prosecutors said.

In Denver, Colorado securities commissioner  Fred Joseph said in a complaint filed in Denver District Court on Tuesday that Jerrald Green received $12.5 million from investors that were supposed to go to real estate investments, but only about $4.9 million of those funds were ever invested, the news agency reported yesterday.

None of the investments have yielded a substantial return, according to Mr Joseph. Mr Green, he said, used money from new investors to pay old investors.

A Denver judge has granted Mr Joseph’s request to freeze Mr Green's assets. Mr Green, who has not been charged with a crime, has denied the allegations and said it's all a misunderstanding, the news agency said.

"Right now, this is just a civil case, but our investigation is ongoing," said Gerald Rome, Colorado deputy securities commissioner.

The Securities Division can refer evidence to prosecutors, who can decide whether to file charges.