Double world sprint champion Kelli White has tested positive for a stimulant not at present on the banned list, International Association of Athletics Federations (IAAF) spokesman Nick Davies said this afternoon.
Davies said White, who is the first American woman to win the world 100-200 double, had tested positive after the 100 metres final on Sunday.
He said that although the stimulant was not on the IAAF's list of prohibited drugs officials were examining the substance involved and would make a statement later on Saturday.
French athletics sources said the drug involved was modafinil. They said it would be put on the banned list next year.
White, 26, was banned from competing in France from January 1 to June 30 this year after testing positive for triamcinolone at last year's Paris Golden League meeting.
Triamcinolone, a drug used to combat asthma, is illegal in France although it is also not on the IAAF banned list. White is scheduled to run in the 4x100 metres relay final on Saturday.