The International Olympic Committee has urged Ukraine to drop threats of boycotting Paris 2024 if Russian and Belarusian athletes compete.
IOC president Thomas Bach has told Ukraine's Olympic Committee that such threats are "extremely regrettable".
In response, Athletes for Ukraine accused the IOC of being "on the wrong side of history".
Ukraine is hoping to gain international support for a ban on athletes from the two countries over Russia's invasion.
The IOC has said it will "explore a pathway" for Russian and Belarusian athletes to compete as neutrals.
Ukraine's sports minister, Vadym Guttsait, who is also president of its Olympic Committee, responded by saying the country could boycott the Paris Games, with several other European nations also calling for the ban to be upheld.
Ukrainian president Volodymyr Zelensky has said allowing Russian athletes to compete at the 2024 Olympics would amount to showing that "terror is somehow acceptable".
In a letter from Bach to Guttsait, the IOC president says comments from Ukrainian officials suggesting allowing Russian and Belarusian athletes would promote the war are "defamatory".
Bach added that threatening a boycott is "premature" because the IOC has not discussed the participation of Russian and Belarusian athletes as neutrals in "concrete terms yet".
He also accused Ukraine of "pressuring" international federations, IOC members and future Olympic hosts "in an attempt to publicly influence their decision making" and claims this has been "perceived by the vast majority of them as, at the very least, extremely regrettable".
Bach said Ukrainian athletes have the "unanimous support" of the Olympic movement and that "we all feel the pain and suffering of the Ukrainian people in this cruel war".
After Russia's invasion of Ukraine in February 2022, the IOC called on sports federations to exclude athletes, officials and teams from Russia and Belarus from international events but Bach has also said he is conscious of the impact such sanctions have on the athletes.
