The under-fire Gatlin has been dropped by his shoe sponsor Nike

The American, 24, is facing a life ban following a second positive drugs test.

Gatlin said in a statement: "I have put my faith in a system that I believe will clear my name and that I believe will allow me to compete again."

Usada announced on Tuesday it had banned him for up to a maximum of eight years pending an arbitration hearing.

Gatlin admitted last month he had tested positive for testosterone at the Kansas Relays on 22 April.

Cheating is completely contrary to who I am Justin Gatlin

He has already had his lucrative contract with Nike suspended until further notice, as has his controversial coach Trevor Graham - who is under investigation by Usada and the IAAF, world athletics' governing body.

Graham's lawyer later told the Reuters news agency that there was no basis for Nike terminating the coach's contract.

"The contract cannot legally be terminated based upon innuendo and suspicion," Joseph Zeszotarski said.

"We hope to avoid having to take legal action but will do so if necessary."

Gatlin said in his statement he still did not know how a banned substance entered his body.

"I have never knowingly used any banned substance, nor have I allowed anyone to administer one to me," he said.

"Cheating, in any form, is completely contrary to who I am as an athlete and a person.

"I expect when that process is concluded that this entire matter will be resolved favourably."

Meanwhile, International Olympic Committee chairman Jacques Rogge has praised Usada's work.

Rogge said: "Usada has provided proof that it produces excellent work - it is a very positive turn in the tide in the battle against doping.

"It may spread doubt in the mind of the public, but it proves that controls are working. The tests are efficient."