Alberto Salazar has insisted that he has never used a banned substance to boost the performance of some of his athletes.

The American coach of Olympic champion Sir Mo Farah has had to defend fresh claims of breaking anti-doping rules following the publication of a leaked report by The Times.

It is claimed in the United States Anti-Doping Agency documents obtained by the publication that Farah and a number of other athletes were given infusions of a research supplement based on the chemical L-carnitine, which is known to have potentially harmful side-effects.

Salazar, the head coach of the Nike Oregon Project, has now hit back at the latest allegations, however, insisting that his methods are perfectly legal and in line with World Anti-Doping Agency guidelines.

"I believe in a clean sport. I have clearly and repeatedly refuted allegations directed against me and the Oregon Project," he told BBC Sport. "I believe in a clean sport and a methodical, dedicated approach to training.

"The Oregon Project will never permit doping and all Oregon Project athletes are required to comply with the Wada Code and IAAF rules. I do not use supplements that are banned. L-carnitine is a widely available, legal nutritional supplement that is not banned by WADA. Any use of L-carnitine was done so within WADA guidelines.

"In this case, to ensure my interpretation of WADA rules was correct, I also communicated in writing with USANDA in advance of the use and administration of L-carnitine with Oregon Project athletes. I have voluntarily cooperated with USANDA for years and met with them more than a year ago.

"The leaking of information and the litigation of false allegations in the press is disturbing, desperate and a denial of due process. I look forward to this unfair and protracted process reaching the conclusion I know to be true."

Farah also hit out at the allegations and admitted to feeling 'deeply frustrated' that the newspaper was attempting to tarnish his reputation.