London — World 100m champion Justin Gatlin says he is "shocked and surprised" by allegations in a British newspaper that his coach and an athletics agent offered to sell performance-enhancing drugs to undercover reporters.

Antidoping officials have launched a probe into the claims in the Daily Telegraph about Gatlin’s coach Dennis Mitchell and an agent, Robert Wagner.

The 35-year-old US sprint star, who has twice served bans for doping, said that he had sacked Mitchell after hearing of the claims.

The report alleged Mitchell and Wagner offered to provide undercover reporters with false prescriptions for performance-enhancing substances and smuggle the drugs into the US. The claims are being investigated by the Athletics Integrity Unit, set up in 2017 by the International Association of Athletics Federations (IAAF) and the US Anti-Doping Agency (Usada).

Gatlin said on Instagram: "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."

He said he was "not using and has not used" performance-enhancing drugs.

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

A spokesman for Usada said the report would be examined carefully. "Investigations stemming from tips and whistleblowers play a critical role in antidoping efforts," a spokesman told the Telegraph.

"We are presently co-ordinating with the Athletics Integrity Unit in order to investigate these claims fully."

IAAF president Sebastian Coe said the claims were
a concern.

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

That came even as the 2017 world champion, who beat Usain Bolt in the 100m final in London in August, had legal advisers release five years of official drugs tests that showed he was clean. Gatlin has long been a controversial figure after being banned for doping in 2001 for one year and in 2006 for four years.

His long-time agent, former sprint hurdler Renaldo Nehemiah, told the newspaper that Wagner had represented Gatlin only two to three times and that Gatlin was not present when banned substances were allegedly discussed with Mitchell or Wagner.

Mitchell and Wagner allegedly offered to supply and administer testosterone and human growth hormone for an actor training for a film on athletics at a price of $250,000, according to the report.

The newspaper said it began its investigation in July after hearing of agents and trainers involved in supplying drugs to athletes.