Heavyweight champion Oleksandr Usyk joins territorial defense battalion in Ukraine

Heavyweight champion Oleksandr Usyk has joined a territorial defense battalion in Ukraine as the nation seeks to defend itself against an invasion from Russia that began Thursday.

The Olympic gold medalist is the latest boxer to take up arms in Ukraine. Usyk's longtime friend, Vasiliy Lomachenko, also joined a territorial defense battalion over the weekend.

Hall of Fame boxer Vitali Klitschko, the mayor of Ukraine's capital, Kyiv, announced he was taking up arms to defend against the invasion on Thursday. His brother, fellow Hall of Famer and former heavyweight champion Wladimir Klitschko, enlisted in Ukraine's reserve army earlier this month in anticipation of the attack.

"If we consider ourselves as brothers, Orthodox ones, do not send your children to our country, do not fight with us," Usyk, ESPN's No. 2 heavyweight, wrote Saturday on Instagram. "Also, I'm addressing this to the President, Vladimir Putin. You can stop this war. Please just sit down and negotiate it with us without claims.

"Our kids, wives, grannies are hiding in the basements. We are here in our own country, we cannot do it any other way. We are defending. Stop this war, stop it. No war."

The former undisputed cruiserweight champion dominated Anthony Joshua via unanimous decision in September to capture three heavyweight titles. The 35-year-old is set to meet Joshua in a rematch in May or June.