The death of Russian citizens in Syria from a US coalition strike last week, which has been played down by both Moscow and Washington, has exposed the role of Russian mercenaries in the multi-front conflict.
The incident followed a steady trickle of reports about Russians dying in battle in Syria while employed as guns for hire in a privately-owned outfit whose role may be securing oilfields for President Bashar al-Assad.
Russia on Thursday has finally recognised that five Russian citizens, not officially affiliated with the Russian military, were likely killed in the strikes in eastern Syria, in the first admission of non-military combat casualties.
The US had said the coalition acted in self-defence when an enemy unit of 300-500 people launched an attack on an established SDF position east of the Euphrates river in Deir Ezzor province.
The coalition warned the Russian military and proceeded to strike the formation, killing up to 100 people. The Russian military said it had no troops in the area.
While US officials have refused to disclose the nationality of the attackers, various reports indicated a death toll of up to several hundred Russians from the strike.
- Who are the mercenaries? -
Russia can legally prosecute mercenaries under an existing law which has been applied against several citizens fighting in Ukraine and Syria in recent years.
In 2014, two Russian men, Vadim Gusev and Yevgeny Sidorov, were sentenced to three years in prison after they recruited over 200 former military soldiers to an outfit called the Slavonic Corps for a trip to Syria's Deir Ezzor.
According to Fontanka website, which has chronicled the involvement of private military contractors in Syria, the Slavonic Corps later became the core of a new mercenary group recruited by former member Dmitry Utkin, nicknamed Wagner.
The Wagner group has no website or social networking page, instead attracting men with military experience through word of mouth.
Utkin and the Wagner group was blacklisted by the US Treasury in 2016 for having "recruited and sent soldiers to fight alongside separatists in eastern Ukraine".
It is known to train at a military base in a village called Molkino outside Krasnodar in southern Russia. According to Fontanka, the Wagner group has fought in Syria since late 2015.
Unlike Gusev and Sidorov, Wagner has not been prosecuted. Instead, he was honoured in the Kremlin in December 2016. Kremlin spokesman Dmitry Peskov said at the time that Utkin was invited as a decorated military veteran.
- Who is behind Wagner? -
According to Fontanka, Wagner is associated with a Russian company Yevro Polis, which has signed a deal with the Syrian government.
Under the deal, the company would capture and secure oil and gas infrastructure in Syria in exchange for a 25 percent share in future resource production.
Fontanka has tied Yevro Polis to the empire of Yevgeny Prigozhin, a Saint-Petersburg businessman running the company Concord Catering which controls several restaurant businesses and has won many contracts from the Russian defence ministry.
Prigozhin, and Concord Catering, were blacklisted by the US Treasury for "having materially assisted" Russian officials and being tied to a company building a military base near Ukraine's border. Yevro Polis is also on the blacklist.
The US special prosecutor investigating Moscow's meddling in the 2016 presidential election indicted Prigozhin Friday for running an influence campaign on the Internet through a "troll farm" company in Saint-Petersburg.
Prigozhin has denied ties both to the Internet company and to Wagner group.
- What's next? -
Mercenaries not directly affiliated with the Russian military may be convenient for Moscow's business interests in Syria while assuring deniability of government involvement.
But after numerous reports of casualties in Syria and capture of two Russians, reportedly from the Wagner group, by IS jihadists last year, Russian officials have called for legalising mercenaries.
Foreign Minister Sergei Lavrov in January said legislation was needed to "protect these people," referring to Russians in private military companies.
"Everybody understands the need for a law," said Mikhail Yemelyanov, an MP in the Just Russia party, who is one of the authors of a bill on private military companies currently being reviewed by government.
Asked if the need was due to Russians fighting in Syria, Yemelyanov told AFP that it's "because it's not just Russians fighting there" and because private military companies are legal in many countries.
Some reports have said that the Russian defence ministry did not know about Russian citizens fighting in the area at the time of the US coalition strike. This would be impossible under the new bill, Yemelyanov said.
"We wrote in the bill that the defence ministry would coordinate and that participation in armed conflicts would only be with their permission," he said.
"If our bill would be passed, everyone would know who is fighting where."