Gancherov's account is one of half a dozen instances Reuters has identified where the Kremlin-linked private military organization that recruited the fighters returned bodies more than seven weeks after the battle and with official documents bearing details that people who knew them say were incorrect.

According to relatives and a battlefield witness, the fighters all died in the clash in Syria's Deir al-Zor region, which took place overnight on Feb. 7.

Such practices, an unusual pattern for Russian fighters killed in Syria, would have helped conceal heavy casualties until after President Vladimir Putin's reelection in mid-March.

Moscow's message at the time was that the military campaign in Syria was a success with only modest human cost.

That details are emerging nearly a year after the Deir al-Zor battle indicates that Moscow may struggle to control its message about casualties abroad at a time when it is expanding its military activities in the Middle East and Africa.

About 100 Russian military contractors were killed in the Deir al-Zor battle, sources have said. The Russian foreign ministry has said that only a handful of Russian citizens were killed there and dismissed reports of heavy losses.