Barnes, the 1996 Olympic gold medalist and the world indoor and outdoor record-holder, and Mitchell, the 1992 Olympic bronze medalist in the 100m, were cited by the sport's world governing body for failing drug tests in April this year.

Sports correspondent Paul Newman on the latest doping scandal

Barnes, who could face a life suspension, was tested in Charleston, West Virginia, and Mitchell in Gainesville, Florida.

Dennis Mitchell could be banned for two years

Mitchell is president of USA Track and Field's Athletes Advisory Committee, the athletes' voice in the national governing body, which has taken a hard stance against drugs.

His suspension was handed down last week and represents his first drug offence.

The International Amateur Athletic Federation has not officially announced the suspensions and the precise terms of the punishment have yet to be determined.

So far, only the first 'A' samples have been tested, but that is sufficient for the IAAF to levy a suspension.

If their 'B' samples are positive, the IAAF will then rule on the severity of the punishment. If the 'B' sample is negative, they are cleared.

Barnes could be banned for life because this is his second offence.

He was suspended for two years starting in 1991 for the banned substance methyltestosterone, a kind of steroid, at an athletics meet in Malmo, Sweden, in 1990.

This time, the substance is androstenedione, a banned nutritional supplement.

Mitchell tested positive for testosterone. If found guilty following the 'B' sample, he probably would receive a two-year ban.