Olympic 100 metres champion Justin Gatlin has been banned for four years for a 2006 positive test for testosterone, the US Anti-Doping Agency (USADA) said on Tuesday.

USADA general counsel Bill Bock said a three-member US arbitration panel, in a 2-1 split decision, had banned Gatlin for four years.

The suspension through to May 24, 2010 could end the career of the 25-year-old Gatlin if he does not successfully appeal to the International Association of Athletics Federations (IAAF) or the Court of Arbitration for Sport (CAS).

The decision has not been released publicly.

The Washington Post reported on its web site that two out of the three American Arbitration Association arbitrators had said they could not give less than a four-year ban because of a previous positive test.

A third dissented, the Post reported.

"It took them five months to come to this? It's ridiculous," his mother Jeanette Gatlin said in a telephone interview from her Pensacola, Florida home.

"I think everybody is blindsided by this opinion."

Gatlin, who has denied knowingly, taking performance-enhancing drugs, still hopes to compete again, his mother said.

"There is no doubt about that," she said. "We will be talking to his lawyer later today."

• Justin Gatlin: Greece lightning

Gatlin could not be reached for comment. His lawyer, John Collins, declined to comment.

Gatlin failed a drugs test in 2001 for a prescribed medication for Attention Deficit Disorder. He was reinstated by the International Association of Athletics Federations the following year.

The American won the 2004 Athens Olympic 100 metres title and completed a 100-200 double at the Helsinki world championships in 2005.

He won each of his five 100 metres competitions in 2006, including tying the then world record of 9.77 seconds in Doha and winning the US title.

But after it was announced that Gatlin had returned a positive test for the male sex hormone testosterone at the 2006 Kansas Relays he was suspended while his case was referred to arbitration.