French investigators suspect that bribes were paid for Rio de Janeiro to be awarded the 2016 Olympic Games, Le Monde newspaper reported on Friday.
The International Olympic Committee said it would contact French authorities over the allegations.
The IOC also said its ethics committee was investigating a payment made to IOC member Frankie Fredericks before Rio was awarded the Games in 2009.
French investigators "have concrete elements to doubt the process to award the Olympic Games. Rio is alleged to have cheated," Le Monde said.
Three days before the IOC awarded the Games to Rio on October 2, 2009, Brazilian businessman Arthur Cesar Menezes Soares Filho paid $1.5 million to the son of shamed former international athletics chief Lamine Diack.
Another payment of $500,000 was made around the same time to another account belonging to the son, Papa Massata Diack, in Russia.
Diack senior, ex-president of the International Association of Athletics Associations, and his son already face bribery charges in France over millions of dollars paid to cover up doping failures by Russian athletes.
The IAAF president is traditionally one of the most powerful members of the IOC.
French prosecutors in the Diack case have already announced that they are investigating the attribution of the 2016 Games to Rio and 2020 to Tokyo. Both cities have denied any wrongdoing.
Rio Olympics spokesman Mario Andrada told AFP that the city was chosen fairly. "The vote was clean," he said.
- IOC notes 'serious allegations' -
Le Monde said investigators have established that a holding company belonging to the Brazilian businessman paid $1.5 million to a company set up by Papa Massata Diack, a marketing consultant for the IAAF.
The businessman subsequently won construction contracts with Rio state linked to Olympics infrastructure.
Le Monde said that on the day of the Olympic vote, Fredericks received $299,300 from Papa Massata Diack's Pamodzi Sports Consulting firm.
The IOC noted the "serious allegations" made by Le Monde, said IOC spokesman Mark Adams, and "remains fully committed to clarifying this situation, working in cooperation with the prosecutor."
"The IOC will be contacting the French Judicial authorities again in order to receive information on which the article in Le Monde appears to be based.
Adams added that Fredericks had "emphasised his innocence" over the Le Monde report and had approached the IOC ethics commission on Thursday.
"The IOC trusts that Mr Fredericks will bring all the elements to prove his innocence against these allegations made by Le Monde."
Adams said Fredericks had explained that money he received from the Diack company was "in connection with the promotion, development of sporting properties in connection with the IAAF marketing Programme, IAAF events and the marketing of the African Athletics Programme 2007/2011.
"Mr Fredericks had a marketing contract with Pamodzi Sports Consulting running from 2007 to 2011."
Adams added that "immediately after a link was made between this contractual payment and the vote for the host city of the Olympic Games 2016, Mr Fredericks himself also turned to the IOC Ethics Commission which is now following up on all the allegations in order to fully clarify this matter."