NEW YORK (REUTERS) - The US Federal Bureau of Investigation and the Securities and Exchange Commission are investigating possible insider trading involving billionaire investor Carl Icahn, golfer Phil Mickelson and Las Vegas gambler William Walters, a source familiar with the matter said.

Federal investigators are looking into whether Mr Mickelson and Mr Walters may have traded illegally on private information provided by Mr Icahn about his investments in public corporations, the source told Reuters, confirming reports on Friday.

Mr Icahn, a legendary activist investor, told Reuters that he was unaware of any investigation and said that his firm always followed the law. He acknowledged a business relationship with Mr Walters but said that he did not know Mr Mickelson personally. "I am very proud of my 50-year unblemished record and have never given out insider information," he said.

Mr Walters and Mr Mickelson play golf together, the source familiar with the investigation told Reuters.

Mr Mickelson said in a statement, "I have done absolutely nothing wrong. I have cooperated with the government in this investigation and will continue to do so.

"I wish I could fully discuss this matter, but under the current circumstances it's just not possible," said the statement, issued through his manager.

The Wall Street Journal cited Mr Glenn Cohen, Mickelson's lawyer, as saying the golfing legend was not a target of the federal probe.

Mr Walters did not respond to requests for comment. Spokespeople for the FBI and the SEC declined to comment.

None of the three men have been accused of any wrongdoing, the source told Reuters.