MOSCOW — Reports about two Russian fighters captured in Syria suggest that the same proxy forces that fight the Kremlin's wars abroad in places such as Syria and Ukraine may also harass members of the Russian political opposition at home.

According to interviews by Russian media with relatives of the men and photographs taken from social media, one of the captured Russians belongs to a hyper-patriotic veterans group and fought in a shadowy private military company whose commanders have received awards at the Kremlin. The other belonged to a pro-Kremlin Cossack paramilitary group whose members have also fought in eastern Ukraine. According to a report by Russian-based OSINT researchers, he was photographed during a "blockade" of supporters of Russian opposition leader Alexey Navalny in April.

The two men are now being held by the Islamic State in Syria. As regime forces with Russian support have advanced in eastern Syria’s Deir al-Zour province, rumors have emerged about Russian soldiers captured or even executed by the Islamic State. High-ranking Russian military officials have been close enough to the front to be at risk, and Russian Lt. Gen. Valery Asapov, who it was revealed also was commanding Syrian troops, was killed last month in a mortar strike near the city.

On Tuesday, the Islamic State released a video through its official Amaq news agency to confirm that it has captured two Russian men. In the 42-second video, the two sat in gray prison uniforms. The one on the left appeared to have been beaten, his right eye swollen shut. The one on the right, bald with a fair beard and possibly handcuffed, spoke.

"I, Roman Sergeyevich Zabolotny, born in 1979," the man said, "was captured during a counterattack by the Islamic State near the town of al-Shula." He then introduced his fellow captive as Grigory Tsurkanu, born in 1978. As his listed details about Tsurkanu's place of residence, he appeared to be reading from a sheet of paper.

It was not immediately clear from the video what the two men were doing in Syria. The Russian Defense Ministry quickly denied that any of its soldiers had been captured, and the Kremlin on Wednesday appeared to support that version of events.

"We've seen the media reports, but they can't be really perceived as official information," Dmitry Peskov, spokesman for Russian President Vladimir Putin, told reporters. "It's some more trustworthy confirmations that will matter."

But in an interview to Radio Svoboda, Tsurkanu's brother, Roman Tsurkanu, explained that the captured Russian had gone to fight in Syria with the private military company Wagner, a mercenary group that has fought in both Syria and Ukraine, according to investigative reports.

"Yes, that's my brother. I don't deny it," Tsurkanu told the news agency, adding that Grigory Tsurkanu was not a soldier. "No, they're mercenaries," he said. "The government is backing a private army, a private military company. Wagner. That's them."

Wagner is led by Dmitry Utkin, a retired lieutenant colonel who, according to media reports published by the St. Petersburg-based site Fontanka, hires former soldiers to deploy as elite infantry in combat zones. Private military companies are illegal in Russia, but it is believed that Utkin's troops have been deployed in Ukraine and Syria to augment Russian forces there and possibly hide their losses.

Utkin and a deputy were photographed with Putin last December at a Kremlin reception, where the two men were among those given awards for fighting in Syria. The Kremlin confirmed that the photo was real but declined to say why Utkin was given the Order of Courage. "Usually they give it for courage," Peskov said.

Later, CIT, an investigative group led by Ruslan Leviev that gathers data from social media, published photos showing Tsurkanu in Syria and Ukraine. In one, he is wearing tan battle fatigues and the blue-and-white striped telnyashka undershirt commonly worn by certain Russian troops (Tsurkanu was formerly in the Airborne Forces). In another of the shots, Tsurkanu is clearly shown standing in front of a sign that says "Lugansk," a city in eastern Ukraine currently under separatist control. His brother, speaking with Radio Svoboda, said Tsurkanu had been to Donbas region of eastern Ukraine twice in 2014, had "received some medals" and had "given it to the Ukrainians good."

The other man, Roman Zabolotny, also fought in eastern Ukraine and Syria as a member of Wagner, a friend told the news website RBC under the condition his name not be released. "We talked for the last time just before he left for Syria," the friend said. "Roman said they pay 300,000 rubles [$5,210] a month."

But perhaps more intriguing than his war record were accusations that he has helped hound opposition supporters of Navalny in Russia between his stints fighting in Ukraine and Syria. "This man was at the opening of Navalny's headquarters in Rostov on April 8th, when [Navalny aide Leonid] Volkov came and they blockaded us in the hotel. A lot of people remember him from then; he was the most active," Anastasia Shevchenko, a Navalny supporter from the city, told RBC.

Photographs posted by the Conflict Intelligence Group appeared to show Zabolotny at the rally, although they have not been confirmed. On his Facebook page, Zabolotny is photographed in a Cossack officer's uniform bearing a patch of the Great Don Cossack Army, one of the first Cossack groups to travel to fight in eastern Ukraine. In Russia, groups claiming Cossack heritage have reasserted themselves as conservative shock troops, pledging to defend Russia against foreign and domestic enemies.