Hamburg - The International Olympic Committee on Monday said it had no reason to doubt swimming super star Michael Phelps' apology after being photographed with a pipe usually used for marijuana consumption.

A photograph of the American was published in an English tabloid on the weekend that showed Phelps using a long glass pipe. The photograph was allegedly taken at a party in South Carolina.

Phelps admitted that he was the person in the photograph, but did not admit to smoking marijuana, nor did he say whether there was any marijuana in the pipe.

Although not considered a performance enhancing drug, marijuana is on the list of prohibited substances and several sportsmen and women have been banned for use of marijuana.

In a statement published on the US Olympic Committee (USOC) website Phelps apologized for his behaviour.

"I engaged in behaviour which was regrettable and demonstrated bad judgment," he said.

"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 IOC's Emmanuelle Moreau told Deutsche Presse-Agentur dpa that her organization had no reason to doubt Phelps' apology.

"Michael Phelps is a great Olympic champion. He apologized for his inappropriate behaviour. We have no reason to doubt his sincerity and his commitment to continue to act as a role model," she said.

Also on Monday USA Swimming issued a statement in which they said they were disappointed with Phelps' behaviour.

"We are certainly disappointed in Michael's behaviour. 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."

USOC had earlier criticized Phelps, saying: "We are disappointed in the behavior 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.

"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."

Phelps last year became the greatest Olympian of all times when he won an unprecedented eight gold medals at the Beijing Olympics, taking his total to 14 gold medals and two bronze medals.

The super star has previously been arrested for driving under the influence of liquor and was given 18 months probation. (dpa)