Би-би-си, Шахты, Ростовская область
The group says it was their volunteers who led the attack on Donetsk airport last month.
During the fierce battle, the insurgents suffered heavy losses. Later more than 30 bodies were repatriated to Russia.
"Different categories of people become volunteers," Yuri explains.
"They can be young people or much older. During the battle for Donetsk airport, one of the volunteers was 56 years old. He showed everyone how it should be done. The country can be proud of people like this.
"Some of the volunteers are quite well off, they've giving up the good life to do this. Others have nothing to lose."
Yuri denies that the Russian government backs the volunteers, or that they receive weapons from the Russian army.
How, then, does he explain reports of separatist fighters riding Russian tanks?
"Russian tanks are like Kalashnikov rifles, you can find them all over the place even as far away as Thailand," Yuri says. "They're very popular for armed conflicts. Yes, they're made in Russia. But who knows how they got there?"Nationalist sentiment
Moscow has repeatedly denied sending troops or military hardware across the border.
But Western governments maintain that among the fighters in eastern Ukraine are professionals funded, equipped and supported by Moscow.
What's more, in recent days Nato and Washington have accused Moscow of massing troops on the border.
"Unfortunately, there is mounting evidence that shows a build-up of Russian military forces near the border with Ukraine," White House spokesman Josh Earnest said on Friday.
"Contrary to the statements by Kremlin officials we do not see any evidence that the Russian military units arriving to the region are connected to any type of border security mission…. We will not accept any use of Russian military forces under any pretext in eastern Ukraine."
It's not only Russian volunteers who have taken up arms.
At a hostel near Rostov I meet a group of Ukrainian citizens, who've fled the violence.
Most of the people here claim to have male family members who've stayed behind in eastern Ukraine to become militants. They blame Ukrainian government forces for the deaths of civilians.
Robert tells me about his son who has become a rebel in their home town of Luhansk.
"I hope my son kills 2,000 of those Kiev bandits," Robert says. "If he does, I'll build a statue to him. He'll be my hero."
Ukrainian President Petro Poroshenko believes his peace plan can end the fighting. But that won't be easy.
This conflict has opened a Pandora's box of nationalist sentiment and hatred which may now be difficult to control.