The former president and director general of the Tokyo 2020 bidding committee have insisted a payment made to an account linked to disgraced former IAAF president Lamine Diack was made for legitimate reasons.
A report in The Guardian alleged the Tokyo bid team made a payment of around EUR1.3millon (£1m) to a Black Tidings bank account in Singapore during the successful attempt to secure the 2020 Olympic Games.
The Black Tidings account was held by Ian Tong Han, a consultant to Athlete Management and Services - a subsidiary of Dentsu Sport set up to market and deliver commercial rights it was granted by the IAAF.
Tan is said to be a close friend of Diack's son Papa Massata Diack - a former consultant for the IAAF who was hit with a lifetime ban from athletics in January following disciplinary hearings over his alleged involvement in a doping cover-up relating to Russian London Marathon winner Liliya Shobukhova.
The elder Diack was IOC president between 1999 and 2013 and was granted honorary membership in 2014.
However, he resigned as an honorary member and left his post as president of the International Athletics Foundation in November last year amid accusations he took bribes to defer doping sanctions against Russian drugs cheats.
French prosecutors are reportedly investigating the payment but Tsunekazu Takeda, former president of the Tokyo bid committee and Nobumoto Higuchi - its ex-director general - have denied any allegations of impropriety.
A statement signed by the pair and released by the Japanese Olympic Committee read: "Media reports have come to our attention claiming misconduct during our activities. We would like to reaffirm that the Olympic Games 2020 were awarded to Tokyo as the result of a fair competition and as a result of the contents of our bid.
"The payments mentioned in the media were a legitimate consultant's fee paid to the service we received from Mr.Tan's company. It followed a full and proper contract and the monies were fully audited by Ernst & Young ShinNihon LLC.
"The Tokyo 2020 Bid Committee can confirm that it paid an amount for the professional services received for the following consultation work including; the planning of the bid; tutoring on presentation practice; advices for international lobbying communications; and service for information and media analysis. All these services were properly contracted using accepted business practices.
"The firm contracted for this work had good credentials and references and were experts on Asian and Arabic and we were fully satisfied with the service we received from them. Furthermore, the amounts paid were in our opinion proper and adequate for the services provided and gave no cause for suspicion at the time.
"This message was conveyed to the IOC when these allegations first surfaced after a request for information from the IOC.
"The activity by the Tokyo bid Committee was at all times fair and correct, and we wish the Tokyo 2020 Organising Committee every success."