Two men shown on a video disseminated by Islamic State jihadists have been identified as Russian by their respective paramilitary associations Wednesday, though it was unclear why they were in Syria.

The video distributed by IS's Amaq news agency on Tuesday shows two handcuffed men sitting in grey robes against a wall. One man appears to have bruises on his face.

A veterans' organisation and a Cossack group on Wednesday identified the men as Grigory Tsurkanu and Roman Zabolotny, although neither said the men were fighting in Syria.

The Russian defence ministry on Tuesday denied any of its enlisted servicemen have been captured. However, the participation of Russian mercenaries in the Syrian conflict has been widely reported.

"This is our active Cossack Roman Zabolotny. We don't know how he ended up in Syria," Lyudmila Bondar, spokeswoman for the Don Cossack Host organisation, told AFP.

Cossacks are a conservative paramilitary association dating back to pre-Soviet times, when they fought for the Russian tsar.

Bondar said Zabolotny is a chef from southern Russia who has worked across the country.

The second man, Tsurkanu, is from the Moscow region, according to Military Brotherhood, a veterans' organisation.

"It pains us to have learnt that Grigory Tsurkanu is in the hands of terrorists in Syria," the organisation said on its website.

- The mercenary system -

In the Amaq video, Zabolotny says that both he and Tsurkanu were captured during an IS counteroffensive near the town of Sholah, in Deir Ezzor province.

Asked about the two men Wednesday, Kremlin spokesman Dmitry Peskov said reports should not to be treated as official information.

"The Kremlin does not have the possibility of concerning itself with their fates," he added.

Russian foreign ministry spokeswoman Maria Zakharova said they are "working on establishing their nationality and location."

"We are trying to find out the reasons why these people were in Syria and the circumstances of their kidnapping," Russian agencies quoted her as saying.

"The work is made difficult as up to this moment there have been no demands made in order to free the hostages."

A series of reports by Russian news website Fontanka has laid out a system for sending willing mercenaries -- most former servicemen -- from Russia to the Syrian conflict through a shadowy outfit known as the Wagner private military group.

Business FM news website on Wednesday cited Roman Tsurkanu as saying his kidnapped brother, who has two children, was a former paratrooper who has been on several missions to Syria with Wagner, most recently in May.

"These contracts are not official," he was quoted as saying.

"They simply turn their backs on people. He will simply be executed now."

Russia stepped into the Syrian conflict in September 2015, backing the Syrian regime of Bashar al-Assad with airstrikes and tipping the balance of the conflict in his favour.

Recently the military said Russian special forces were participating on the ground in the offensive against IS.

Source: AFP