World indoor 1,500 metres record holder Regina Jacobs has been banned for four years after a positive test for the anabolic steroid tetrahydrogestrinone (THG).

In a statement on Saturday the United States Anti-Doping Agency (USADA) said 40-year-old Jacobs, who announced her retirement on Thursday, had accepted the sanction after a positive test at last year's U.S. trials.

Her subsequent results will now be annulled and she will forfeit all her winnings since testing positive on June 21, 2003.

THG is at the centre of the BALCO doping scandal that has engulfed U.S. athletics.

An arbitration panel was scheduled to hear Jacobs's case on Sunday, the same day as the final of the U.S. Olympic trials' women's 1,500 metres. Instead of entering the competition, in which she would have been the favourite, Jacobs decided to retire.

Jacobs, the 2003 world indoor 1,500 metres champion, was one of six U.S. athletes entered in the trials facing doping charges.

World 100 metres record holder Tim Montgomery failed to finish in the top three, thereby missing selection.

Olympic 400 metres silver medallist Alvin Harrison failed to make the final and his twin Calvin finished fifth.

Former world indoor 200 metres champion Michelle Collins withdrew from the trials. Olympic 4x100 metres relay gold medallist in 1996, Chryste Gaines failed to qualify for the 100 and later withdrew from the 200.

The eliminations and withdrawals helped ease an awkward problem for U.S. officials. They have vowed to send a clean team to Athens but were facing the possibility of selecting athletes who were still facing doping charges.