World 100m champion Gatlin in new doping scandal

'These allegations are extremely serious and I know the independent Athletics Integrity Unit will investigate in accordance with its mandate.'

World 100 metres champion Justin Gatlin said on Tuesday he is "shocked and surprised" at doping allegations made against his coach Dennis Mitchell, like Gatlin a convicted doper, but added that he sacked him as soon as he heard about the issue.

Britain's Daily Telegraph set up a sting where they claim Mitchell, the American former medal-winning sprinter who was previously banned for doping, and sports agent Robert Wagner had offered to supply performance-enhancing drugs to undercover reporters claiming to be making a movie featuring a doped athlete.

Gatlin, 35, who won the world title in London this year against a backdrop of jeering relating to his two doping bans, issued a statement via Instagram where he said: "I am not using and have not used PEDs (performance-enhancing drugs.

"I was shocked and surprised to learn that my coach would have anything to do with even the appearance of these current accusations. I fired him as soon as I found out about this.

"All legal options are on the table as I will not allow others to lie about me like this."

The Athletics Integrity Unit and the US Anti-Doping Agency (USADA) have both said they are investigating the claims.

USADA said in a statement: "Investigations stemming from tips and whistleblowers play a critical role in anti-doping efforts. We are presently co-ordinating with the Athletics Integrity Unit in order to investigate these claims fully."

The International Olympic Committee said on Tuesday: "The IOC has full confidence that WADA will look very carefully into this matter."

The Telegraph quoted International Association of Athletics Federations president Seb Coe as saying: "These allegations are extremely serious and I know the independent Athletics Integrity Unit will investigate in accordance with its mandate."

In a statement to the Telegraph, Mitchell, who confessed on oath to using banned substances during his career, said: "I never suggested in any way that any of my current athletes used any banned substances or that I was familiar with training any of my current athletes with those substances."

Wagner also denied being involved in doping but said he "played along" in the sting because he knew what was going on.

Gatlin has been a divisive figure in the sport throughout his career, which brought him Olympic 100m gold in 2004 and a host of other global medals. He served two doping bans for offences he has always denied and after his second comeback, was widely painted by the media as the bad guy going up against the sport's darling, Usain Bolt.

In August, in Bolt's final individual championship race, Gatlin took the 100m gold at the World Championships in London, with the Jamaican finishing third.