IAAF staff members repeatedly confronted then president Lamine Diack on delays of disciplinary proceedings against six Russian athletes who had violated anti-doping rules, and resisted approaches to have them compete at the 2013 world championships in Moscow.
A report seen by dpa on Monday also says that staff members alerted the IAAF ethics committee in April 2014 about corruption allegations around the cases - four of them dating back to before the London 2012 Olympics.
The IAAF employees referred the cases to the Court of Arbitration for Sport (CAS) in July 2014 without notifying their superiors when they still remained unresolved.
But the athletics' ruling body also insisted "there is no systematic corruption within the IAAF" in the detailed answer sent Friday to an independent commission of the World Anti-Doping Agency (WADA).
The 35-page comments respond to the commission report from November which alleged widespread doping in Russian athletics and the covering up of positive doping tests for money, and led to the suspension of the Russian federation from the IAAF in December.
The IAAF ethics committee last week banned Diack's son and two Russian officials for life, and imposed a five-year ban on former IAAF anti-doping director Gabriel Dolle over blackmailing a Russian athlete to cover up a positive doping test.
Diack, his son and his lawyer, and Dolle are also the target of a French criminal investigation into the affair.
The IAAF, in the comments, said that "no doping case has been covered up by the IAAF" but acknowledged "unexplained and suspicious delays" in the results management before the athletes were ultimately sanctioned.
It insisted that "only a very small number of individuals formerly associated with the IAAF are believed to have been involved in the alleged corruption" and that it "is not aware of any other interference ... in the work of its medical and anti-doping department."
The issue was first made public by German broadcasters ARD in December 2015. A second WADA commission report is scheduled to be made public on Thursday.