Former heavyweight boxing champions Vitali and Wladimir Klitschko say they'll go to war for Ukraine against Russia

• Ukraine's army will be able to call on the services of two former world heavyweight champion boxers.
• Vitali Klitschko has vowed to join his brother, Wladimir, in fighting for Ukraine against Russia.

The former heavyweight boxing champion Vitali Klitschko said he would take up arms alongside his brother and fellow boxing icon, Wladimir, to fight for Ukraine, their home country, against invading Russia.

Russian President Vladimir Putin launched a military assault in Ukraine Thursday.

Attacks have so far been reported on Ukrainian military targets in the cities of Kharkiv, Kyiv, and Odessa, killing dozens.

Vitali, who has been the mayor of Ukraine's capital, Kyiv, since 2014, said he was ready to fight in a "bloody war."

"I don't have another choice, I have to do that. I'll be fighting," the former WBO, WBC, and Ring Magazine world heavyweight champion told ITV's Good Morning Britain on Friday.

"I believe in Ukraine, I believe in my country and I believe in my people."

Wladimir, who boasts the second longest reign as a heavyweight champion in boxing history, enlisted in Ukraine's reserve army earlier this month.

In a statement made on LinkedIn Thursday, he too said he would fight and urged others to do the same.

"Democracy cannot defend itself; it needs the will of the citizens, the commitment of everyone," he wrote. "Basically, there is no democracy without democrats.

"Here, we will defend ourselves with all our might and fight for freedom and democracy. You can also act. Let not fear seize us; let's not remain frozen."

The 45-year-old went on to ask the world's governments to impose swift and serious sanctions upon Russia.

"This war against my country is not only the result of one man's madness, but also the result of years of weakness in Western democracies," he said.

"This madness must be stopped now by stepping up deterrents. Our governments need to say things loud and clear."

The two brothers also appeared in a joint video calling for international support for the Ukrainian cause.

The Klitschko brothers aren't the only Ukrainian professional boxers affected by Russia's invasion.

Vasiliy Lomachenko, a two-time Olympic gold medalist and three-division champion, fled Ukraine for Greece, according to MARCA.

WBA, WBO, and IBF heavyweight champion Oleksandr Usyk, who defeated Anthony Joshua in September, was in London this week attending a publicity event for a video game, but returned to Ukraine Thursday.

"Some wrote to me that I ran away; I didn't, I was at work but I'm back, I'm home," Usyk said in an Instagram video.

"Friends, we have to unite because it's a hard time right now and I'm really emotional and worry about my country, and our people. Friends, we have to stop this war; all of us together."