Track and field's world governing body is investigating Justin Gatlin's coach for alleged doping violations.

The International Association of Athletics Federations said today the probe into the activities of Trevor Graham will be carried out in conjunction with the US Anti-Doping Agency.

At least six athletes who trained under Graham have received doping suspensions.

Gatlin, the Olympic and world champion and co-world record holder in the 100 metres, tested positive for testosterone or other steroids after a relay race in Kansas in April.

Gatlin, who denies knowingly using banned substances, faces a life ban if found guilty of what would be a second doping offence.

Graham has always denied direct knowledge or involvement with drug use.

He operates Raleigh-based Sprint Capitol USA, a team of about 10 athletes that includes Gatlin.

Graham has claimed Gatlin was the victim of a massage therapist who rubbed testosterone cream on the sprinter's legs without his knowledge after the race.

Graham is reportedly under investigation in connection with the BALCO steroid probe. If evidence is found that he engaged in doping practices, USADA will initiate disciplinary proceedings against him, the IAAF statement said.

"In order to defend the credibility of our sport, we will engage all our efforts, in co-operation with partners such as USADA, to defend the majority of athletes who are clean, against athletes, coaches, managers or any other support personnel who break our anti-doping rules," the statement said.

Despite the probe, eligible athletes coached by Graham remain free to compete in this year's remaining World Tour meets based on invitations from organisers, the IAAF said.

Organisers of a meet in Berlin, Germany, have banned all athletes linked to Graham from competing in the September 3 event, and called on other meets to do the same.

Graham helped launch the federal investigation of the Bay Area Laboratory Co-Operative three years ago by anonymously mailing a syringe containing a previously undetectable steroid to USADA.

The US Olympic Committee has barred Graham from using its training centres and training sites as a result of his suspected links to doping.

Graham's lawyer on Tuesday asked the USOC to lift the ban, saying the coach passed a lie-detector test when he denied giving performance-enhancing drugs to athletes.

AP