Los Angeles - Olympic 400 metres champ LaShawn Merritt of the United States has been suspended after testing positive for an anabolic steroid contained in an over-the-counter penis enlargement product.

Merritt, who is also the world champion at 400 metres, said in a statement via his lawyer that he was "deeply sorry" at failing three doping controls for the banned substance DHEA.

The 23-year-old American, who faces a two-year ban, said: "To know that I've tested positive as a result of a product that I used for personal reasons is extremely difficult to wrap my hands around.

"I hope my sponsors, family, friends and the sport itself will forgive me for making such a foolish, immature and egotistical mistake. Any penalty that I may receive for my action will not overshadow the embarrassment and humiliation that I feel inside.

"I am deeply sorry and hope that other athletes who take these types of over-the-counter products will be even more cautious and read the fine print, because if it can happen to me, it could happen to you."

Merritt failed tests for the steroid dehydroepiandrosterone (DHEA) between October last year and January after he started taking the product following the end of last season.

DHEA is a steroids precursor banned by the US Anti-doping Agency.

"He has now put his entire career under a cloud and in the process made himself the object of jokes," said USA Track and Field chief executive Doug Logan, who added he was "disgusted by this entire episode."

The Virginia-born athlete has accepted a temporary ban and will not compete until his case has been heard, his lawyer Howard Jacobs stated.

USADA declined to comment saying it wanted to wait until the investigation was complete.

The USADA probe can last months and usually an athlete guilty of a first-time doping offence receives a two-year ban.

The American followed up his Beijing Games gold medal by dethroning two-time 400m defending champion Jeremy Wariner when he strode to an impressive victory at last year's World Athletics Championships in Berlin.

As well as winning his individual titles at both Beijing and Berlin he also helped his country win the 4x400m relay titles at both events.