The combatants, who appear to number in at least the hundreds, describe Putin as the enemy, even as they take up arms against their countrymen. They range from captured Russian soldiers to political dissidents like the 30-year-old Russian who asked to be called Yan, an IT worker who now spends his days scouting, identifying potential artillery targets and bringing medical supplies to Ukrainian soldiers on the front.

“No Russian should have crossed the border with a weapon in his hand,” Yan tells TIME from a district near the Ukrainian capital, Kyiv, where he has served in the country’s territorial defense forces since the war started at the end of February. “I am here to oppose Russian aggression and also defend Ukraine.” He produced a valid Russian passport but requested the pseudonym out of fear for the safety of his family in Russia. He said he moved to Kyiv from Russia’s Ural mountains three years ago, fearful of imprisonment after his office was raided. A self-described anarchist, Yan had taken part in demonstrations against Putin’s rule.

“Vitya” is the nom de guerre chosen by a 25-year-old Russian political science student who said he also joined the Ukrainian territorial defense forces to continue his fight against the Russian government, having attended anti-government protests in his native Moscow since his early teens. “I love my motherland,” Vitya says from Kyiv, where he is stationed. “Hopefully this war will break the political regime. I would like to return home one day.” He said his parents, who are in the Russian capital, know their son is in Ukraine but think he is donating blood and helping the Ukrainian war effort in other ways.