Mo Farah's coach Alberto Salazar claims those accusing him of doping are 'knowingly making false statements'.
The BBC and US website ProPublica released material last week claiming Salazar had given Farah's training partner Galen Rupp banned anabolic steroid testosterone.
Salazar vigorously denied all of the allegations in a statement:
I have said all along that I believe in a clean sport, hard work and I deny all allegations of doping. The BBC and ProPublica have engaged in inaccurate and unfounded journalism, with a complete lack of regard for both Galen and Mo.
Given the time and effort the BBC and ProPublica committed to making these false allegations I hope that media and fans will afford me a short time to show the accusers are knowingly making false statements.
I will document and present the facts as quickly as I can so that Galen and Mo can focus on doing what they love and have worked so hard to achieve.
Ed Warner says if he was a close friend of Mo Farah's he would advise the Olympic champion to suspend his relationship with Alberto SalazarRead the full story ›
Mo Farah's rival Andy Vernon was 'not surprised' the 32-year-old did not show up at Birmingham Grand Prix on Sunday.
Speaking after the 5000-metre race in which he finished ninth, Vernon said: "I'm pretty sure his mind won't be in the right place for racing and being an athlete I know how important that sort of thing is.
"Also... he's Mo Farah, he's expected to win."
Vernon and Farah have enjoyed a difficult relationship following a social media spat last year.
Olympic champion Mo Farah has pulled out of today's 1500m race at the Diamond League event in Birmingham saying he is "emotionally and physically drained".
"This week has been very stressful and taken a lot out of me. I have not been able to focus properly on today's race," Farah said in a statement.
"I want to run well in the IAAF World Athletics Championships in Beijing and have decided it is better for me to go back to the US, seek answers to my questions and get back into training."
"I apologise to the people who bought tickets to come and watch me race and ask for your understanding at this time."
Farah will not be ending his relationship with Alberto Salazar as he has not seen 'clear evidence' to back up doping allegationsRead the full story ›
Mo Farah has said doping allegations concerning his coach Alberto Salazar is "ruining my reputation" - but he has no plans to end their relationship.
The double Olympic gold medallist told a press conference he has not seen "any clear evidence" that Salazar had been involved in doping.
"I'm a clean athlete, against drugs and anyone who isn't should be banned for life.
"I want to know the answers and the easiest thing to do would be to jump.
"But if you can't show me proof (Salazar), I'm out. I will be talking to people because it's my reputation", he added.
"The headline is 'Mo coach' and it's not fair on my family, kids. I want the memories, the 75,000 people cheering for me at the Olympics. They should know."
UK Athletics has 'absolutely no concerns' over the conduct and coaching methods of Alberto Salazar in relation to Mo FarahRead the full story ›
There is enough evidence for investigation into Mo Farah's coach Alberto Salazar over drug allegations World Anti-Doping Agency boss says.Read the full story ›
Mo Farah has claimed his Great Britain team-mate Andy Vernon questioned his nationality after the double Olympic champion won European 10,000 metres gold last summer.
Farah made the claims when he was questioned on Friday about a Twitter spat the pair had earlier in the week.
The 31-year-old, who was born in Mogadishu in Somalia before moving to Britain as a child, has apologised for the social media row, but admitted their past contributed to his frustrations boiling over.
Vernon has admitted making the comments in Zurich, but insisted they were intended as "a joke" among a group of people "having a laugh" saying:
I said it on a table full of people and we were all having a joke at the time. We had just raced and the team was all in high spirits. The whole table was having a joke and a laugh and it was just a comment to carry on the jokes. He laughed at the time. If he did take it out of context it wasn't meant that way and I apologise.