Usain Bolt says doping scandals have set sprinting back

Jamaican sprinter Usain Bolt, right, stretches out to win the men's 200-meter race, during the Athletics Diamond League meeting at Stade de France stadium, in Saint Denis, north of Paris, Saturday, July 6, 2013. Other sprinters are from left: Jamaican Warren Weir, France's Christophe Lemaitre, Jamaican Nickel Ashmeade. (AP / Remy de la Mauviniere)

LONDON -- Usain Bolt says the recent doping scandals in sprinting have set the sport back, while insisting he is not a cheat.

Tyson Gay, Asafa Powell and Sherone Simpson are among a number of athletes to fail recent tests ahead of the world championships next month.

Bolt says "it's going to set us back a bit," adding that he hopes to "help people forget what has happened" with his own performances and stressing: "I am clean."

The Jamaican said he has had one text-message exchange with compatriot Powell since the former 100-meter world record-holder tested positive for the stimulant oxilofrone.

Bolt told him "to stay strong."

Bolt was speaking in London where he competes on Friday for the first time since his three gold medals at the Olympics a year ago.