For the past year, the Kremlin has strenuously denied that its troops are supporting pro-Russia rebels in eastern Ukraine — but fighters on the ground are apparently no longer bothering to keep up the farce.

St. Petersburg native Dmitry Sapozhnikov, who went to Ukraine in October to fight alongside the rebels, told the BBC Russian service in a candid interview from Donetsk that Russian military units have played a decisive role in rebel advances, including the operations in February that led to the capture of the transport hub of Debaltseve. Russian officers directly command large military operations in eastern Ukraine, he noted.

"Tanks and Russian units came through the LPR," Sapozhnikov said, referring to the self-declared Luhansk People's Republic on the border with Russia. "But I don't think that this is a secret anymore, everyone admits it, and the Russians admit it.… Thanks to the Russian forces, we're able to take positions quickly. We were located near Debaltseve and thinking, well, we're going to hold them in this encirclement for another month, it will drag on.… But in the end we took it in three days."

Sapozhnikov said that tank units from Siberia were aiding the rebels. His account corresponds with an interview given by an injured Russian soldier in a hospital in Donetsk to the independent newspaper Novaya Gazeta, in which he said that his tank unit had helped take Debaltseve.

Throughout the conflict, which the United Nations says has killed more than 6,000 people, evidence of Russian military support for the rebels has mounted. Ten Russian paratroopers were captured in Ukraine last August, and NATO published satellite photographs showing what it described as Russian tanks crossing the border that summer. Rebel leader Alexander Zakharchenko even admitted around the same time that active-duty Russian troops were fighting with his men, though he claimed that they had chosen to fight while on vacation.

Russian officials including President Vladimir Putin have repeatedly denied that their soldiers are in Ukraine, arguing that the Russians who are fighting there are all volunteers.

Sapozhnikov himself is one such volunteer, a leader of a fringe monarchist party in St. Petersburg who said he left his business renovating homes to help defend Russian speakers in eastern Ukraine and oppose Kiev's shift toward the West. As the leader of a special forces unit of the Donetsk People's Republic, he also took part in the bloody battle for the Donetsk airport, which the rebels captured in January after months of fighting.

He admitted the Russian military has been instrumental to their success.

"Naturally, all operations, especially large-scale ones like encirclements, are directed by Russian soldiers, Russian generals," Sapozhnikov said. "They make plans together with our commanders. I often had to go to the headquarters to provide some information."

The Novaya Gazeta interview with tank crewmember Dorji Batomunkuev, who was recovering from severe burns that left his hands and face covered in bandages, offered further details about how Russian soldiers have been secretively deployed to Ukraine.

Drafted into the army in 2013, Batomunkuev was placed in a newly created battalion last fall. The battalion's 31 tanks and their crews were sent to the border region of Rostov, ostensibly for training, but Batomunkuev said that he knew they would be sent to Ukraine. They painted over the emblems and numbers on their tanks, removed the patches and chevrons from their uniforms, and turned in their passports, phones, and military IDs. After three months of exercises, they were sent forward one day and only realized that they had crossed into Ukraine when they started seeing road signs for Donetsk.

"We understood that the whole war depended on us," he said. "That's why they'd beaten the training into us those previous three months. We were well prepared, both our snipers and other troops."

The unit eventually was deployed near Debaltseve, where it shelled Ukrainian positions. Batomunkuev was injured when an enemy shell hit his tank. Although he sympathized with the conscripts on the Ukrainian government side, he also argued that Ukrainian forces had killed civilians and hired "mercenaries" from Poland and Chechnya.

Batomunkuev called Putin "crafty" for denying that he had sent troops to Ukraine, and stressed that Kiev's turn to the West was endangering Russia's interests.

"From what I've read and the history I've studied, Russia's opinions have started to be reckoned with in recent years," he said. "Nowadays, we're on the rise again, we are being treated with contempt again, but we haven't disintegrated yet."

Asked why the Kremlin has continued to deny the presence of its soldiers in Ukraine, Sapozhnikov said that he thought there might be a "secret agreement" between Russia, the European Union, and the United States to look the other way. He expressed that Putin was likely using the same strategy that he employed with the annexation of Crimea in March: initially denying the deployment of Russian troops, then admitting it once the territory had been won.

"If the EU and the USA wanted to prove that Russia's forces are located here, I think it would be easy to do," Sapozhnikov said. "They would just go and photograph the armor and everything. But they're not doing that, they're closing their eyes. And the Russians for their part close their eyes to the presence of American and European soldiers on the Ukrainian side."

He claimed that 300 foreign soldiers, including Americans and Europeans, had been captured in Debaltseve, and that "most of them were snipers" — although he admitted that he hadn't seen any of them himself.

Although the US and United Kingdom have sent military advisors to Ukraine this year, and a handful of European volunteers have been known to be fighting on Kiev's side, no Western combat troops have been reported. The West has also been sending non-lethal military supplies to Ukraine, including a shipment of US Humvees that arrived last week.

Sapozhnikov also said that his unit had been preparing earlier this month for a potential assault on Mariupol, a strategic port city that pro-Russia forces briefly held last year. Although the ceasefire declared in February has been mostly observed in recent weeks, Kiev worries that the city will be the next target of separatist forces.

"We're going to fight until we free the territory of Donbas," Sapozhnikov said, referring to the coal-mining area that comprises the Donetsk and Luhansk regions. "I hope that happens in the near future, but I'm ready to be here for another year or two."