Olympic gold medallist Sir Mo Farah has maintained his innocence and said he a "clean athlete" after a leaked report implicated him in using illegal performance-enhancing drugs.

The US Anti-Doping Agency (Usada) report, dated March 2016, said Farah's coach Alberto Salazar gave him and other athletes, who trained at the Nike Oregon Project in north-west America, infusions of the chemical L-carnitine, among others.

Farah was among the athletes who used the drug over prescribed limits, according to the report, but the superstar says he did "nothing wrong".

In a statement posted on his Facebook, Farah said: "It's deeply frustrating that I'm having to make an announcement on this subject.

"I am a clean athlete who has never broken the rules in regards to substances, methods or dosages and it is upsetting that some parts of the media, despite the clear facts, continue to try to associate me with allegations of drug misuse."

Usada has confirmed the veracity of the report acquired by the Sunday Times, but said it was premature to label Farah as a drugs cheat until it was officially established by the anti-doping body.

The organisation said it prepared the report in response to a legal request from a state medical licensing body, which oversees physicians.

Mo Farah Salazar
Mo Farah with coach Alberto Salazar who is also implicated in the leaked Usada report. Getty

"We understand that the licensing body is still deciding its case and as we continue to investigate whether anti-doping rules were broken, no further comment will be made at this time," a spokesman for Usada said in a statement.

"Importantly, all athletes, coaches and others under the jurisdiction of the World Anti-Doping Code are innocent and presumed to have complied with the rules unless and until the established anti-doping process declares otherwise. It is grossly unfair and reckless to state, infer or imply differently."

In his statement, Farah called on Usada to publish any findings it had on wrongdoing to avoid any further speculation.

Farah said: "As I've said many times before we all should do everything we can to have a clean sport and it is entirely right that anyone who breaks the rules should be punished.

"However, this should be done through proper process and if Usada or any other anti-doping body has evidence of wrongdoing they should publish it and take action rather than allow the media to be judge and jury."

Clinical research has shown that L-carnitine, the amino acid Salazar is accused of giving his athletes, increases helps to reduce heart rates and increase running speed and endurance levels.