World 100 metres 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.

Anti-doping officials have launched an investigation into the claims about Gatlin's coach Dennis Mitchell and an agent Robert Wagner, while IAAF President Seb Coe says changes are needed.

"We are looking at who we want in our sport," Coe, the 1500m gold medallist from the 1980 and 1984 Games, said in a statement.

"The IAAF recognises as an industry we need to do more," said the Englishman.

"Focusing on the influences that surround athletes is a critical area of work," Coe insisted.

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

The report alleged Mitchell and Wagner offered to provide undercover reporters with false prescriptions for banned performance-enhancing substances and smuggle the drugs into the United States.

The claims are being investigated by the Athletics Integrity Unit (AIU), set up this year 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 have not used" performance-enhancing drugs.

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

IAAF president Sebastian Coe said the claims were concerning.

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