Rugby Europe President and International Olympic Committee member Octavian Morariu Posted on Twitter: "Even though I hoped that this news won't be confirmed, unfortunately, I can now sadly say that Oleksi Tsibko, former captain of the Ukrainian national team, former President of the Ukrainian Rugby Union and also Mayor of Smela City died defending his town and his country.
"May he rest in peace and be always remembered."
World Rugby President Sir Bill Beaumont tweeted: "On @UN #SportsDay, our thoughts are with the Ukraine rugby family who are facing such incredible challenges at present.
"We also remember those who have been victims of the recent violence, including the former union President Oleksii Tsibko.
"We stand with Ukraine in condemning this needless violence and will continue to offer solidarity and friendship."
Ukraine's former water polo captain Yevhen Obedinsky was also confirmed to have died in the fighting this week.
Inside The Games reports Obedinsky was killed on March 17 in the Russian siege of Mariupol.
It comes after it was last week confirmed Ukrainian kickboxing world champion Maksym Kagal was killed while fighting in the besieged city of Mariupol.
His coach said last week that Kagal, 30, died as be battled Russian forces as part of Ukraine's Azov Battalion unit.
Many Ukrainian athletes have taken up arms to defend their country against the Russians. Retired tennis star Alexandr Dolgopolov returned home to defend his native city Kyiv.
Fellow former tennis player Sergiy Stakhovsky, who famously beat Roger Federer at Wimbledon in 2013, also signed up for his country's military reserves.
Others to answer their country's hour of need are two-time Olympic boxing gold medallist Vasiliy Lomachenko and world heavyweight champion Oleksandr Usyk, who returned to fight as soon as the invasion began.
Former heavyweight boxing champion Vitali Klitschko is the mayor of Kyiv and said before the war started he was ready to fight. The 50-year-old's brother Wladimir, also a former heavyweight champion, volunteered to take part in the resistance.