Four U.S. track and field athletes have had their back-up B test samples confirmed as positive for the new designer steroid THG, a spokesman for the sport's governing body says.

The International Association for Athletics Federations confirmed on Wednesday that the samples taken from the athletes matched initial A samples which were made known last month.

The four, who have yet to be named officially, are entitled to an appeals hearing before the U.S. Anti-Doping Agency prior to a possible two-year ban.

The samples were taken in June at the U.S. Track and Field Championships at Stanford University, an IAAF spokesman said.

A fifth athlete, Britain's European champion 100 metres sprinter Dwain Chambers, was suspended on Friday after UK Athletics confirmed that a positive test for THG was supported by the results of his B test.

He has denied ever knowingly taking banned substances or in any way trying to cheat.

Last month it was reported widely in the U.S. that world indoor 1500 metres record holder Regina Jacobs and hammer thrower John McEwen had also tested positive for THG.

THG was previously unknown to testers but an anonymous tip-off led to a Californian university lab discovering a way of detecting the "designer" steroid this year.

It led to the series of positive tests sparking fears that next year's Athens Olympics could be stripped of a host of banned big-name athletes.