Olympic swimmer Michael Phelps admitted that he had engaged in "regrettable" behavior 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."

Bob Bowman, Phelps' longtime coach and mentor, had little to add.

"Michael has issued his statement. He regrets his behaviour and I'm sure he'll learn from this experience," Bowman said in a statement of his own. "I'm glad to have him back in training."

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.

USA Swimming, the national governing body for the sport, said it was disappointed by Phelps' admission.

"We are certainly disappointed in Michael's behavior. Our Olympic champions are role models who are looked up to by people of all ages, especially young athletes who have their own aspirations and dreams," USA Swimming said in a statement.

"That said, we realize that none among us is perfect. We hope that Michael can learn from this incident and move forward in a positive way."

The US Olympic Committee also expressed disappointment in the swimmer, who on January 22 was named the USOC's Sportsman of the Year for making Olympic history in Beijing by collecting the most golds won by any athlete at a single Games, giving him a career total of 14 golds.

He also set seven world records in Beijing.

"We are disappointed in the behaviour recently exhibited by Michael Phelps.

"Michael is a role model, and he is well aware of the responsibilities and accountability that come with setting a positive example for others, particularly young people. In this instance, regrettably, he failed to fulfill those responsibilities," the USOC said.

"Michael has acknowledged that he made a mistake and apologized for his actions.

"We are confident that, going forward, Michael will consistently set the type of example we all expect from a great Olympic champion."

The News of the World claimed Phelps 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."

Source: AFP