With the Athens Olympics less than a year away, the world governing athletics body announced on Tuesday it would re-test all urine samples from August's Paris World Championships after the discovery in the U.S. of a previously undetectable "designer steroid".

The central sport of the Olympic Games has never fully recovered from the Johnson scandal, when the Canadian was stripped of his 100 metres gold medal after testing positive for the anabolic steroid stanozolol.

The following year, Johnson told a Canadian government inquiry he had been taking performance-enhancing drugs since 1981.

Athletics has struggled since to rid itself of a tainted image and the discovery of the "designer steroid" tetrahydrogestrinone (THG) comes as a shuddering body blow to the sport's administrators.

The International Association of Athletics Federations' (IAAF) decision to re-test all Paris samples follows an announcement by the U.S. Anti-Doping Agency (USADA) last Thursday that several American athletes had tested positive for THG -- a steroid that has been tweaked by chemists to make it undetectable under normal testing.

The positive samples were found in the re-testing of 350 doping samples from the U.S. athletics championships in June. The USADA said the discovery was the largest drug-bust in sport.

The USADA received an initial tip from a coach who sent them a syringe containing THG.

The federal jury investigation is probing the finances of the San Francisco area nutritional supplement maker which the USADA suspects is the source of THG, the Bay Area laboratory Co-operative (BALCO).

BALCO was founded by nutritionist Victor Conte, who is now its president.

BALCO has a client list including a host of elite athletes, among them the sprinter Marion Jones, winner of a record five Olympic medals in Sydney, her partner Tim Montgomery, the 100 metres world record holder, and baseball's Barry Bonds.

Bonds, New York Yankee first baseman Jason Giambi and world 100m and 200m champion Kelli White have been subpoenaed to testify, the San Francisco Chronicle reported on Monday.