Training bases, border crossings, and burials on the sly -- the southern Russian region of Rostov has been buzzing with reports of covert military activity since conflict broke out in neighboring eastern Ukraine last spring.

Now, a prominent Russian magazine says militants maimed in the conflict are being treated at a secretive facility in the provincial capital, Rostov-on-Don, the latest evidence that separatist fighters are being quietly transferred across the border for care.

Rostov-based journalist Yelena Romanova says she has discovered a makeshift clinic caring for men who lost limbs while fighting government forces in eastern Ukraine, where more than 6,400 people have been killed and some 16,000 wounded since April 2014.

Her article, which appeared on June 1 in The New Times, features interviews with recovering fighters and photos of maimed patients.

"This is an underground rehabilitation center for people injured in the fighting," she wrote. "Most of those brought here have lost limbs. Most of them are Ukrainians."

The report casts further doubt on Russia's repeated denials of involvement in the conflict.

According to Romanova, the clinic is located in a detached house in a quiet neighborhood of Rostov-on-Don.

She says local residents sounded the alarm after spotting ambulances with Ukrainian number plates and wounded men hobbling around the neighborhood on crutches.

Romanova's article says one of the "coordinators" running the clinic, a man identified as Igor, agreed to let her in only after she agreed not to ask for surnames or take pictures of patients' faces.

He reportedly told her that the clinic was currently treating 34 men and had seen some 150 patients in total.

He refused to reveal how the facility was funded, saying only that it relied on private donations.

Romanova was able to interview several patients, including a 46-year-old electrician from Donetsk, a provincial capital held by the separatists, who joined their ranks a year ago.

"At first we stood at checkpoints with clubs, if anyone had a shotgun it was for 5-10 men," the man, who gave only his nickname, Shpil, was quoted as saying. "Then we received weapons."

Shpil said that his hand was blown off in a shelling attack in August close to the town of Ilovaisk, the site of major fighting, and that he had been brought to Rostov to get a prosthetic limb.

The patients reportedly include at least one fighter who is from Russia, not Ukraine.

Romanova says she spoke to Vasily, who identified himself as a volunteer from Russia's Sverdlov region who lost his leg in a mine explosion less than one week after reaching his unit close to Donetsk.

Journalists from Radio Rostov were able to visit the clinic, too, after airing an interview with Romanova.

They said they found out that the enterprise was funded chiefly by businessmen from Moscow and the Karelia region, in northwestern Russia, to the tune of $3,700 a month.

RFE/RL reported on a similar facility in Azov, a city in the Rostov region, in February.

Two dozen Ukrainian separatists were receiving treatment there at the time.

The clinic had also been set up in a private home. And like their peers in Rostov-on-Don, the patients had no idea who was footing their medical bills.

Despite severe wounds, some patients in Azov said they were eager to return to the front lines.

"As soon as I get my prosthesis, I will go back," said Volodymyr Fesenko, a militant from the eastern Ukrainian town of Rovenky. "There are many people like me there, and they still fight."