Pettigrew (left) was part of the USA's winning team in Sydney

Ex-Olympic champion Antonio Pettigrew has admitted he was on drugs when he helped deny Britain a gold medal at the 1997 World Championships.

The 40-year-old was part of the USA quartet that beat Roger Black, Iwan Thomas, Jamie Baulch and Mark Richardson into second in Athens.

On Thursday Pettigrew admitted to taking performance-enhancing drugs.

He was speaking at the trial of coach Trevor Graham, who has denied charges of lying to federal authorities.

The court in San Francisco heard Pettigrew testifying that Graham encouraged him to inject human growth hormone and EPO, both banned substances, from 1997.

Pettigrew said he soon began buying the drugs from Angel Heredia, an admitted steroids dealer, and his performance showed a remarkable improvement as a result.

"I was running incredible times as I was preparing for track meets," Pettigrew said during 30 minutes of testimony. "I was able to recover faster."

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The USA team of Pettigrew, Chris Jones, Tyree Washington and Jerome Young edged out Britain by just 0.18 seconds in 1997.

US Olympic Committee chief executive officer Jim Scherr said. "If an athlete who ran in the finals knowingly and purposely engaged in cheating, the medals won by the entire team are tarnished and, in our view, should be returned."

But Scherr said any decision to strip Pettigrew of his medals rests with the International Olympic Committee (IOC) and the International Association of Athletics Federation (IAAF).

Pettigrew won gold in the 4x400m relay at the Sydney Olympics in 2000 alongside Michael Johnson and brothers Alvin and Calvin Harrison.

The IOC tried to strip the team of their Olympic gold medals after Young, who was part of the team but did not run in the final, tested positive for drugs and was banned for life.

But the Court of Arbitration for Sport overruled the IOC and said the entire team should not be disqualified, allowing Pettigrew to keep his medal.

Pettigrew also won relay gold at the 1999 and 2001 World Championships and in 1998 he was part of the USA team that set the world record of 2:54.20 that still stands.

He also beat Britain's Black by five-hundredths of a second to win the 400m at the 1991 World Championships in Tokyo, although there is no evidence to suggest he was taking performance-enhancing substances at that stage of his career.

He retired from athletics in 2002 and is an assistant coach at the University of North Carolina.