Athletics Kenya's chief executive has asked to step aside for 21 days pending an investigation into allegations that he sought bribes to reduce the doping bans of two Kenyan athletes who failed drugs tests, the federation confirmed on Tuesday.

Isaac Mwangi last week dismissed as "fabrication" accusations by Joy Sakari and Francisca Koki Manunga that he had asked each athlete for $US24,000 to reduce their four-year bans. The two runners were caught doping in August at the world championships in Beijing, where Kenya topped the medals table.

Athletics Kenya (AK) officials on Tuesday showed journalists a letter from Mwangi that stated "The allegations have caused me a lot of mental anguish."

"I am anxious to have my name cleared," he added, according to the letter dated February 15.

Kenya is a global leader in endurance running, both on the track and in big-city marathons, but more than 40 of its athletes have been banned for doping in the past three years.

The spike in doping, coupled with corruption allegations against top AK officials over the past year, has stoked fears in Kenya that the East African nation could follow Russia and be suspended from global athletics.

The doping crisis in Russia and Kenya, as well as allegations of corruption within the world governing body, the IAAF, have cast a shadow over the sport ahead of the Rio Olympics in August.

Jack Tuwei, the AK president, said the newly formed Anti-Doping Agency of Kenya (ADAK) would conduct the investigation into allegations against Mwangi and report findings in two weeks.

"If cleared, (Mwangi) will come back," said Tuwei.

He added that the World Anti-Doping Agency (WADA) and the IAAF Ethics Commission had been in touch about the allegations.