American sprinter Calvin Harrison has been suspended for two years for a second doping violation and will be ineligible for the Athens Olympics, the U.S. Anti-Doping Agency (USADA) said on Monday.

Harrison, a gold medallist in the 4x400 metres relay at the 2000 Sydney Games, tested positive for the banned stimulant modafinil at the 2003 U.S. national championship, the USADA said in a statement.

Harrison's first doping offence occurred at the 1993 U.S. junior national championships, which also involved a prohibited stimulant.

He had been named to the preliminary 4x400 metres relay pool for Athens after finishing fifth in the individual event at last month's Olympic trials.

Harrison was not immediately available for comment but in an October 2003 telephone interview with Reuters admitted testing, "positive for modafinil at the nationals".

He said a coach in California had given him this pill and he had taken it.

"He (the coach) emphasised that it was not on the banned substance list and assured me that it was not an illegal substance," Harrison said.

Harrison's suspension is effective July 26, the date of his arbitration hearing before a three-member panel of the American Arbitration Association (AAA)/North American Court of Arbitration for Sport (CAS), USADA said.

The doping agency said Harrison would lose all competitive results and winnings from June 21, 2003, the date of his positive test for modafinil, including his second place finish in the 400 metres at the 2003 U.S. championships.

Harrison also could lose his gold medal from the Sydney Olympics because of a doping case involving fellow American 400 metres runner Jerome Young.

The International Association of Athletics Federations (IAAF) recommended last month that all members of the U.S. 4x400 metres relay team lose their gold medals from Sydney.

The ruling followed a CAS decision that Young should not have been eligible for the 2000 Games because of a 1999 doping positive.