The American coach of Olympic champion Mo Farah may have broken anti-doping rules to boost the performance of some of his athletes, says a leaked report.
Alberto Salazar has been under investigation since a BBC Panorama programme made allegations about drugs use at his US training base.
A leaked US Anti-Doping Agency (Usada) report, dated March 2016, has been obtained by the Sunday Times.
Salazar and Briton Farah deny they have ever broken anti-doping rules.
The leaked report also alleges Salazar, head coach of the world famous endurance Nike Oregon Project (NOP), routinely gave Farah and other athletes legal prescription drugs with potentially harmful side-effects without a justifiable medical reason.
The investigation into Salazar, who is also a consultant to UK Athletics (UKA), has been under way since at least June 2015.
The Usada interim report was passed to the Sunday Times by the suspected Russian hacking group Fancy Bears.
The BBC has so far been unable to verify its authenticity with Usada, or establish whether any of its reported conclusions are out of date.
Contents of the report
According to the Sunday Times, the leaked report claims that Salazar:
- used a banned method of infusing a legal supplement called L-carnitine;
- risked the health of his athletes, including Farah, by issuing potentially harmful prescription medicines to improve testosterone levels and boost recovery, despite no obvious medical need.
Salazar maintains that drug use has always fully complied with the Wada code and that athletes were administered with L-carnitine in "exactly the way Usada directed".
The Sunday Times claims the Usada report also reveals:
- investigators have been impeded because Salazar and several athletes have "largely refused to permit Usada to review their medical records";
- Farah received an infusion of the legal supplement L-carnitine in 2014, which Usada is continuing to investigate in case the method of infusion broke doping rules by going over the legal limit of 50ml.
The report, apparently written in March 2016, allegedly states: "Usada continues to investigate circumstances related to L-carnitine use" by Farah.
Farah, who has won 5,000m and 10,000m gold at the past two Olympic Games, told The Sunday Times two years ago that he had "tried a legal energy drink" containing L-carnitine but "saw no benefit" and did not continue with it.
The revelations will pile more pressure on Britain's greatest ever endurance runner, who has steadfastly refused to end his association with Salazar.
It raises questions too for UKA, which gave the Briton the all-clear to continue working with Salazar after an inquiry was launched following the BBC Panorama programme.
In June 2015, in conjunction with the US website ProPublica, the BBC's Panorama programme Catch Me If You Can made a series of allegations about the methods at NOP, and included testimony from a number of former athletes and coaches, including Kara Goucher and Steve Magness.
The film alleged Salazar had a fixation on the testosterone levels of his athletes, and may have doped American Olympic medallist Galen Rupp with the banned steroid version when he was 16. The programme also alleged Salazar had conducted testosterone experiments on his sons to see how much of the drug he could apply to them before it triggered positive tests.
The film also alleged Salazar used thyroid medicine inappropriately with his athletes, and encouraged the use of prescription medication when there was no justifiable need.
Salazar denied the wrongdoing alleged in the programme, and issued a 30,000-word rebuttal.
Usada took the unusual step of confirming it had launched an investigation into NOP following the BBC and ProPublica's revelations in 2015. Earlier stories by the New York Times and the Sunday Times had also raised concerns about some of Salazar's methods.
It is not clear why the Usada report remains unpublished.
The BBC has sought comment from Usada, Alberto Salazar, Sir Mo Farah and UK Athletics.