Athletes from Ukraine and other nations have called on the International Olympic Committee (IOC) to suspend Russia and Belarus and ban their athletes from events immediately.
Ukraine's health ministry said on Sunday that 352 civilians, including 14 children, had been killed since Russia's invasion of the country last week. Belarus has been a key staging area for the invasion.
Russia calls its actions in Ukraine a "special operation".
"Russia's invasion of Ukraine, supported by Belarus, is a clear breach of the Olympic and Paralympic Charters -- a breach that must be met with strong sanctions," the athletes said in an open letter to IOC President Thomas Bach and International Paralympic Committee (IPC) chief Andrew Parsons.
The letter, released by the Global Athlete movement, which aims to empower athletes, said that Ukrainian sportspeople and their families in the country were in "grave danger" and it had been a challenge to speak to them as they were in bomb shelters.
It added that refusing to take swift action and suspend the National Olympic Committees of Russia and Belarus would send the wrong message.
"Your lack of action will send a message to every athlete in the world that you have chosen Russia and Belarus interests over athlete interests. Your legacy will be defined by your actions," the letter said.
The letter received widespread support, including from British former marathon runner Paula Radcliffe and Canadian former cross-country skier Beckie Scott.
The IOC has said international sports federations should either move or cancel sports events currently planned in Russia or Belarus, while the IOC's executive said Russian and Belarusian national flags should not be displayed at international sports events.
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