The deaths of as many as 200 members of the so-called "Wagner Group" in Syria last month shone a light on the mysterious private army used there by Russian President Vladimir Putin.
Questions had already been raised on the role of the group in the Syrian conflict and intensified when the US said on February 7th it had killed at least 100 pro-regime troops in Deir Ezzor.
US-backed Syrian Democratic Forces (SDF) came under sudden attack by the pro-regime forces, and heavy US airstrikes and artillery fire repelled the assault.
After days of silence, Moscow acknowledged five Russian nationals were killed and "dozens" wounded in the attack, saying they all were in Syria "on their own initiative".
At the time of the attack in Deir Ezzor, the Russian defence ministry insisted it had no servicemen in the eastern province of Syria.
However, numerous reports have confirmed that many Russian citizens are fighting in Syria as mercenaries working for the Wagner Group.
Various media outlets have reported up to 200 fatalities in the Deir Ezzor battle. The independent group of Russian investigative bloggers known as the Conflict Intelligence Team (CIT) has established the identities of dozens of them -- all members of the Wagner Group.
'Russia's shadow army in Syria'
"Wagner can and should be regarded as Russia's shadow army in Syria, as it has been providing the vital frontline component to Russia's operations in Latakia and Eastern Syria," CIT's Kirill Mikhailov told AFP.
Pavel Baev, an associate research fellow at the French Institute of International Relations, said Russia's resort to "shadow armies... has the double benefit of ensuring deniability and discounting casualties".
But "the problem with assets like the Wagner Group is that they are never fully controllable and could become maverick", he said.
Wagner was set up by former Russian military intelligence officer Dmitry Utkin, who was part of the first convoy of Russian mercenaries sent in autumn 2013 to Syria.
But their ill-equipped mission, which did not have the backing of the Russian authorities, ended in fiasco.
They engaged in some combat with the "Islamic State of Iraq and Syria" (ISIS) but rapidly returned to Russia, where two backers of the scheme were jailed for three years for mercenary activities.
Utkin reappeared in Syria in autumn 2015, when Russia launched an intervention in support of Kremlin ally Bashar al-Assad's regime.
In December 2016, the former intelligence officer showed up at a televised ceremony held in the Kremlin to honour "the Heroes of Fatherland" and was the same day photographed alongside Putin.
Various media reports in Russia and the US said Wagner is being funded by one of Putin's allies -- Evgeny Prigozhin, a Saint Petersburg businessman who made a fortune in the catering business before signing lucrative contracts with Russia's military and the government.
'No mourning period'
Despite attempts to keep Wagner's activities in Syria quiet, details have trickled out in embarrassing ways.
Last year, for example, ISIS released a video that claimed to show captured Russian citizens, who were later linked to Wagner, the Washington Post reported February 23rd.
Several Wagner personnel were captured on audio recordings discussing the February 7th attack in Deir Ezzor. They used explicit language to describe the incident, indicating their government had failed them.
The death of Russian mercenaries has provoked further grief, as well as anger that the Russian government does not acknowledge their sacrifices.
"They just threw them into battle like pigs," said Yelena Matveyeva, the widow of Stanislav Matveyev, a 38-year-old mercenary from Asbest who is also believed to have died.
"Wherever they sent them, they had no protection," Matveyeva told RFE/RL, according to the Guardian.
She said Russian authorities should acknowledge citizens who die fighting in Syria, and where possible, help to repatriate bodies.
In a daily press call this month, Dmitry Peskov, the Kremlin spokesman, was asked by a reporter if there would be a day of mourning for the Russians killed in the February 7th airstrike.
"Because of what? I do not get why a mourning period needs to be declared," Peskov said.
The number of Wagner's fighters in Syria has been the subject of debate by analysts and media, with online magazine Republic.ru reporting the presence of 2,500 mercenaries in March 2016.
It said $350 million had been spent on mercenaries since the operation began.
Wagner's mission "is essentially a failure", a former member of the group told Russian weekly Sovershenno Sekretno.
He said 40% of recruits had been jailed for serious crimes before they joined Wagner and would refer to each other as the "unlucky ones".
This "low-quality" of recruits, along with the idea that Wagner functioned as an autonomous army and accepted missions from non-Russian groups, led to rising tensions with officials both on the ground in Syria and in Moscow's corridors of power.
In early 2016 the group lost the trust of -- and financing from -- Russia's defence ministry, according to various reports.
This led "Prigozhin to seek other contracts, such as the one with Damascus whereby Wagner would liberate oil and gas fields and infrastructure in exchange for 25% of production", he added.
To this end, he established a company named Evro Polis, which signed the contract with Assad's government in December 2016 and is now responsible for paying Wagner mercenaries' salaries of an estimated $3,500 to $5,000 per month.