Double world sprint champion Kelli White and five other American athletes have tested positive for the stimulant modafinil, the U.S. Olympic Committee (USOC) announced on Tuesday.

White, sprinter Chryste Gaines, hurdlers Sandra Glover, Chris Phillips and Eric Thomas, and hammer thrower John McEwen tested positive at either the U.S. or World Athletics Championships, the USOC said in a statement.

White, like her fellow athletes, is contesting the case but could be stripped of both her 100 and 200 metres world titles. The first American woman to win the sprint double, she said she had been prescribed the drug to treat narcolepsy, or sleepiness.

McEwen also failed a test for the designer steroid tetrahydrogestrinone (THG).

The discovery of the previously undetectable steroid touched off an international doping scandal involving not only athletics but U.S. professional baseball and football as well.

Top track athletes Tim Montgomery and Marion Jones and baseball star Barry Bonds have testified before a federal grand jury in San Francisco that is investigating a California laboratory suspected of being the source of the steroid.

The USOC said that White failed tests for modafinil at both the U.S. and World championships.

Its announcement is the first official confirmation of her positive test at June's U.S. championships. The IAAF had already announced that she tested positive for the stimulant after winning the world championships' 100 metres in Paris in August.

White's case and those of the other five athletes are under review by the U.S. Anti-Doping Agency (USADA).

Gaines and 400-metre hurdlers Glover and Thomas failed a test for the stimulant at the American championships while Phillips, a 110-metre hurdler, tested positive for modafinil at the world championships, the USOC said. McEwen failed tests for both modafinil and THG at the U.S. championships.

He is the first American to be named as testing positive for the steroid.

Previously, U.S. officials had said there were four American positives for the steroid without giving details. Britain's European 100 metre champion Dwain Chambers has been identified as testing positive while U.S. media reports have named world indoor 1,500 metre record holder Regina Jacobs.

The USOC added that cyclist Adham Sbeih tested positive for erythropoietin (EPO) at the U.S. Cycling Federation (USCF) Elite Track National Championships in August.

"USADA's Anti-Doping Review Board determined that sufficient evidence of doping exists to proceed further in seven cases," the USOC said.

"All seven athletes are disputing their cases."