International Olympic Committee (IOC) president Thomas Bach has called on Ukraine to drop threats of a boycott of the 2024 Olympics over the participation of Russian and Belarusian athletes.
Ukraine hopes to secure widespread international support for a ban on Russian and Belarusian athletes after the IOC opened the door for them to compete as neutrals in Paris.
Athletes from Russia and neighbouring Belarus, which aided Moscow's invasion of Ukraine a year ago, have been banned from many international competitions since.
Ukrainian President Volodymyr Zelensky has urged the IOC to ban Russia from the Olympics, and Olympic bodies and lawmakers in the Nordic and Baltic regions have backed Ukraine.
In a letter to Ukraine's National Olympic Committee (NOC) president Vadym Huttsait, seen by Reuters, Bach said claims that allowing Russian and Belarusian athletes back into the Games would promote the invasion were "defamatory".
The IOC has said a boycott will violate the Olympic Charter and that its inclusion of Russian and Belarusians is based on a U.N. resolution against discrimination within the Olympic movement.
"The participation of neutral athletes with a Russian or Belarusian passport at the Olympic Games Paris 2024 has not even been discussed in concrete terms yet," Bach said.
"Therefore, your letter... to your fellow NOCs, to the International Federations, IOC Members and to future Olympic hosts, pressuring them in an attempt to publicly influence their decision making, has been perceived by the vast majority of them as, at the very least, extremely regrettable.
"It is the responsibility of every NOC... to uphold the fundamental principles of the Olympic Charter."
The IOC announced last month that athletes from the two countries might be allowed to earn slots for the Olympics through Asian qualifying and compete as neutrals, with no flags or anthems.
In a joint statement, Ukrainian athletes said they cannot accept the IOC's attempts to "unite the entire world in peaceful competition" by welcoming Russian and Belarusian athletes back into the Olympic Movement.
"The letter to President Guttsait states that 'Ukrainian athletes can continue to count on the full solidarity from the entire Olympic Movement.' What solidarity is the IOC offering with this decision?" the athletes said.
"Solidarity is unity with a common interest — there is no interest amongst Ukrainians to see war criminals attend the Games under the mask of a neutral flag.
"Uniting the world through peaceful competition is a utopian view that denies the role of sport in geopolitics and disregards the way sport is routinely used as a tool of authoritarian states."
They added that the IOC was "rewarding (Russian president Vladimir) Putin's aggression" and that the Olympic body "must choose a side" in the war.
"The IOC continues to be on the wrong side of history and their letter is further evidence of the power Russia has over the organization and the Olympic Movement," they added.
"Sponsors, host cities, and national governments must stop tolerating the IOC's kowtowing to Russia. The time for the IOC to be held accountable is now."
Paris mayor Anne Hidalgo has said it is inconceivable to have Russian athletes marching as a delegation while "bombs are still raining down on Ukraine".
"There are no plans for a Russian or Belarusian delegation or the flags of these countries at the Olympic Games Paris 2024," the IOC said in a separate statement on Thursday.
"The only option that could be considered are individual, neutral athletes."
Paris 2024 organisers have said they will abide by the IOC's decision on the issue.