Nigerian sprinter Davidson Ezinwa was found to have traces of hCG, a banned hormone which helps produce testosterone.

He was disqualified from seventh place in the semi-finals of the 100m and now faces a two-year ban as the drug is regarded as a serious offence by the IAAF.

It was Ezinwa's second positive test. In February 1996, he and his twin brother, Osmond, both received three-month bans for the use of the stimulant ephedrine.

Ezinwa, 27, was the 1990 world junior champion in the 100m and a bronze medalist at 60m in the 1997 World Indoor Championships. He was sixth in the 1996 Olympics 100m final.

'Minor offence'

The other offender was Somali 1,500m runner Mohamed Ibrahim Aden of Somali, who tested positive for the stimulant ephedrine.

He was disqualified from sixth place in his semi-final but will receive only a warning, not a ban, as his offence was regarded as minor.

The build-up to the championships was marred by a number of high-profile cases of athletes testing positive for banned substances.

Big names

They included Jamaican sprinter Merlene Ottey, winner of more Worlds medals than anyone in history, and former Olympic 100m champion Linford Christie of Britain.

Both tested positive for nandrolone, a controversial drug also implicated in the case of British sprinter Doug Walker, who was cleared by UK athletics officials but remains banned by the IAAF.

In addition, Cuban high jump world record-holder Javier Sotomayor, tested positive for cocaine.