The 100m runner was tested during the Canadian team's pre-championships camp in Calgary.

It was announced in Edmonton on Tuesday that her sample contained traces of the banned anabolic steroid stanozolol.

"We are going to have our share of bad apples as well as those in other countries," World Anti-Doping Agency chief Dick Pound said.

"As a nation we are certainly very much committed to doing what we can.

"It indicates the fight against doping in sport is clearly not over. We are going to have to be more vigilant, more aggressive in going after people who cheat."

The drug is the same one that caused the downfall of Canadian sprinter Ben Johnson after he had won the Olympic 100m final in Seoul in 1998.

Clarke, who like Johnson was born in Jamaica, had failed to qualify from the heats on Monday having won her national championships.

The 34-year-old, from Oshawa, in Ontario had made remarkable progress recently.

But she had put that down to a revolutionary new programme involving eastern philosophy.

Joanne Mortimore from Athletics Canada said: "We are very disappointed to have a positive test.

"It does show that the Canadian anti-doping system is working."