Double Olympic champion Mo Farah has insisted he is "100 per cent clean" but admitted he would sever all ties with Alberto Salazar if doping allegations against the coach were proven.

Farah, who won both the 5,000m and 10,000m at the London Olympics, insists it is not fair he is being accused by association, saying the stain is "killing him", but believes Salazar is entitled to be treated as innocent until found otherwise.

"I am not on anything, trust me," he said.

"To be labelled something you are not and labelled a cheat is not fair and right: if I am a cheat prove I am a cheat or leave me alone. Prove I am crossing the line.

"Let's get to the bottom of this. It is killing me, killing my family."

Farah has not been accused of wrongdoing himself, but has been under the spotlight since BBC Panorama and US investigative website ProPublica made allegations against Salazar, saying he violated several anti-doping rules including using testosterone medication on Farah's training partner Galen Rupp when he was 16 in 2002.

Salazar last week issued a lengthy rebuttal of almost 12,000 words denying the allegations and Farah, who has met with Salazar to discuss the situation, wants to believe his coach while backing the investigations under way by UK Anti-Doping and USADA.

"UK Anti-Doping and USADA need to get on top of this and deal with it properly as it is overshadowing athletics," Farah said.

"They are just allegations. If there is wrongdoing I will be the first person to run (away) but you have to give people a chance in life and the benefit of the doubt."

Farah admits he was stunned when the allegations came to light and it preyed on his mind so much he pulled out of Birmingham's Diamond League meeting at the last minute.

Having done so he immediately jumped on a plane to quiz Salazar in Portland.

"I was shocked. I couldn't believe what I saw. I am the first person to say 'Look, what's going on?', I wanted answers," he told Sky Sport.

"I work so hard for what I do. It has taken me half of my life to achieve what I achieved and for people to think I am taking a shortcut is not right, it's not fair. This picture has been painted of me. I am 100 per cent clean.

"I want to continue winning medals but I want people to know I am 100 per cent clean and am not on any drugs.

"This picture of me as a cheat is not right, it's not fair. Why me?

"I said 'You need to assure me'. He said 'Mo, I am working on this, I will come out and disprove these allegations. These are just allegations and I can prove this to you'.

"I believed in him. He (now) needs to prove it to the public and people.

"I want those people (making allegations) to go to the right authority - not the media where words get twisted - and I am glad UK Anti-Doping and USADA are looking at the investigation."

Farah reiterated, however, that should Salazar be found guilty he would not hesitate to cut all ties immediately.

"Alberto has coached me and helped me; there is no question I have won medals with Alberto," he said.

"But if he has crossed the line and is proven to have done so then I am out, trust me. Why would I be there?"

Although no allegations were made against Farah, subsequent to the airing of the Panorama documentary it emerged the 32-year-old had missed two drugs tests prior to the 2012 Olympics - a third missed test would have left him at risk of a ban.

But Farah believes the story was unfair.

"A lot of athletes miss tests but it doesn't come to the public eye," he said. "So why me? I've taken 148 tests since 2007 and 103 tests since the 2012 Olympics and every single one has been negative. I can't win."