AFP

London, Feb 2: Olympic swimmer Michael Phelps admitted on Sunday that he had engaged in "regrettable" behaviour and "demonstrated bad judgment" after a photo was published that appeared to show him smoking cannabis.

A British newspaper, the News of the World, published the photo allegedly showing the multiple Olympic gold medal-winner inhaling from a glass pipe which is generally used to smoke the drug.

"I engaged in behaviour which was regrettable and demonstrated bad judgment," Phelps said in a statement.

"I'm 23 years old, and despite the successes I have had in the pool, I acted in a youthful and inappropriate way, not in a manner that people have come to expect from me.

"For this, I am sorry. I promise my fans and the public -- it will not happen again."

The newspaper said the picture was taken on November 6, almost three months after Phelps won an historic eight gold medals at the Beijing Olympics, when he went to a party at the University of South Carolina.

It claimed he was visiting Jordan Matthews, a girl he was secretly dating who was a student at the university, and threw himself into a series of parties in houses and bars.

The photograph shows Phelps, wearing a white t-shirt and a baseball cap back to front, holding the pipe -- known as a bong -- to his lips and apparently inhaling.

The tabloid quoted a partygoer as saying: "You could tell Michael had smoked before. He grabbed the bong and a lighter and knew exactly what to do.

"He looked just as natural with a bong in his hands as he does swimming in the pool. He was the gold medal winner of bong hits.

"Michael ended up getting a little paranoid, though, because before too long he looked like he was nervous and ran out of the place."

Phelps was recently named the US Olympic Committee Sportsman of the Year for making Olympic history in Beijing by collecting the most golds won by any athlete at a single Olympics, giving him a career total of 14 golds.

He also set seven world records in Beijing.