FRANKFURT -- A group of athletes led by Olympic discus champion Robert Harting has released a video message saying track and field's world governing body had "betrayed" them by not doing enough to fight doping.

"Dear IAAF, we cannot trust you anymore," Harting said in the English-language video posted on YouTube. "We have to act now."

Harting, a three-time world champion who won Olympic gold in London in 2012, has been a vocal critic of the International Association of Athletics Federations. He declined to be considered for the IAAF's "Athlete of the Year" award in 2014 because he did not want to appear alongside candidates who have served doping bans, including U.S. sprinter Justin Gatlin.

The IAAF responded by inviting Harting to its offices or one of the competitions to see personally the federation's fight against doping and what it is doing in "rooting out the cheats and protecting the credibility of competition."

"The IAAF very much appreciates and admires the passion, commitment and strength of opinion of all clean athletes and their feeling of intense frustration following the recent unfounded media accusations concerning the IAAF's anti-doping program," the Monaco-based federation said in a statement.

"Therefore we would love to welcome Robert Harting, whose no-nonsense anti-doping stance we greatly admire, to come and talk to us so we can address his concerns," the IAAF added.

The Harting video comes after reports by German broadcaster ARD and The Sunday Times newspaper in Britain that blood doping was rampant in the sport, citing leaked test results from an IAAF database. The IAAF has strongly rejected suggestions that it had failed to follow up on the suspicious tests and that it wasn't doing enough to uncover doping.

The media reports examined the results of 12,000 blood tests involving 5,000 athletes from 2001 to 2012, and concluded that 800 were suspicious. The reports said that 146 medals -- including 55 golds -- in disciplines ranging from the 800 metres to the marathon at the Olympics and world championships were won by athletes who have recorded suspicious tests.

"You damage our sport," U.S. shot putter Eric Werskey says in the video.

Harting's girlfriend, discus thrower Julia Fischer, holds up a handwritten message saying: "You broke my childhood dreams."

"You put money over athletes," says hammer thrower Kathrin Klaas, while 800-meter runner Robin Schembera adds: "I want to run against clean athletes, not monsters."

Harting concludes with the message, "You betrayed my beliefs."

The athletes say they demand "honesty, integrity, transparency."

They hold up signs with (hashtag) hitIAAF.

The doping reports were published ahead of this month's world championships in Beijing, which the IAAF said is "causing stress and confusion" for athletes.

The World Anti-Doping Agency is investigating the claims made by ARD, and the IAAF said it is "comfortable that an independent, impartial assessment of the data and the follow-up action by the IAAF will now be made by the competent authority."

The IAAF hit back at two scientists whose findings led to allegations this week of widespread doping in the sport, saying Saturday that their assertions are "seriously incorrect."

In a scathing statement, the IAAF said the two Australian anti-doping scientists, Michael Ashenden and Robin Parisotto, were wrong to claim that the governing body didn't act on suspicious blood profiles and "had no knowledge whatsoever of the actions taken by the IAAF."