Vasiliy Lomachenko, a former three-division world champion and two-time Olympic gold medalist with eyes on a title bout in June, has reportedly taken up arms to defend his native Ukraine against the Russian invasion.

Lomachenko, 34, posted an image of himself wearing military fatigues and holding a rifle via Facebook on Sunday alongside an announcement that he has joined a voluntary defense battalion amid the Russian onslaught.

"The Belgorod-Dniester Territorial Defense Battalion has been formed and armed," the caption reads, per Google translate. "Boxer Vasyl Lomachenko is in the defense, said Mayor Vitaliy Hrazhdan."

Lomachenko's post went live amid the fourth day of fighting in Ukraine after Russian President Vladimir Putin launched a military attack on the neighboring nation and its people targeting the capital city Kyiv and other strategic locations. Belgorod-Dniester is a port city in southwest Ukraine near the Black Sea.

ESPN reports that Lomachenko left his home near Odessa for Greece when the invasion began on Thursday, but has since returned to be with his family. Ukrainian news outlets Hromadske and Ukrinform reported that he'd joined the defense battalion.

Lomachenko joins Klitschko in Ukraine's fight

Lomachenko isn't the first world-renowned Ukrainian boxer to come to his country's defense. Retired WBO and WBC heavyweight champion Vitali Klitschko is now the mayor of Kyiv. An outspoken Putin critic, Klitschko is also a leader in Ukraine's defensive efforts against the Russian attack. As is his brother Wladimir, a fellow former world heavyweight champion who has joined Vitali in the Ukrainian Army reserves.

“I don’t have another choice,” Vitali told "Good Morning Britain" last week of taking up arms against Russia. “I have to do that.”

Lomachenko, meanwhile, is not retired. One of the world's top-rated pound-for-pound boxers, he agreed this month to face lightweight champion George Kambosos in a title fight on June 5 in Melbourne, Australia, according to ESPN. The fight's official announcement was pending agreement from Kambosos. Now the fate of the fight rests with a cause much larger than boxing.

As a professional, Lomachenko has won world championships as a featherweight, junior lightweight and lightweight. He has twice represented Ukraine at the Olympics, bringing home gold from Beijing in 2008 and again from London in 2012.

WBC Ukraine president Mykola Kovalchuk applauded the boxers' stances in a statement to ESPN.

"We are so proud of our boxers, our real champions in boxing and champions in this war," Kovalchuk told ESPN. "We are proud to be Ukrainians."

Where are Russian forces surrounding Ukraine? Check out this explainer from Yahoo Immersive to find out.