Olympic 100 metres champion Justin Gatlin will challenge his four-year suspension for a positive doping test in 2006, his attorney said on Wednesday.

"We are going to have to continue to fight because Justin has not done anything wrong," John Collins told Reuters by telephone from his Chicago office.

Collins said Gatlin's options includes appealing to the International Association of Athletics Federations (IAAF), taking the case to the Court of Arbitration for Sport (CAS) or filing a federal lawsuit.

"We are looking at all of them and may do all or some percentage of them," Collins said.

A three-member arbitration panel suspended the 25-year-old American until May 2010, but left open the possibility of adjusting the sanction.

Under IAAF rules Gatlin has 30 days to file a notice of appeal to CAS.

Collins said he hoped the matter could be resolved in time for Gatlin to compete in June's US Olympic trials for this year's Beijing [Images] Olympics [Images].

REDUCED BAN

Gatlin, the 2005 world 100 and 200 metres champion, tested positive for the male sex hormone testosterone at the 2006 Kansas Relays.

He could have received an eight-year ban because the 2006 case was his second failed test.

But the arbitration panel said the case appeared to be unique, encouraging Gatlin to ask the IAAF to review his initial positive test in 2001.

Should the IAAF or the 2001 review panel find Gatlin was not at fault, his four-year ban could be adjusted, the arbitrators said.

Gatlin tested positive in 2001 for an amphetamine contained in a medication he had taken since childhood for Attention Deficit Disorder. He was suspended for two years but the IAAF later found Gatlin had not intentionally committed a doping violation and reinstated him after one year.

Gatlin argued that the 2001 case should not count as a doping offence but the majority of the arbitration panel, in a 2-1 decision, disagreed.

US Anti-Doping Agency chief executive officer Travis Tygart said the punishment is fair.

"The four-year penalty issued by the arbitration panel is a fair and just outcome," Tygart said in a statement.

Collins said he found the process disappointing.

"They put this burden of proof [of no fault] on the athlete that is impossible to meet," he said.