On December 9, the Kremlin marked the Day of Heroes of the Fatherland with a lavish event attended by "more than 300 military personnel and civilians who have demonstrated particular courage and heroism, including Heroes of the Soviet Union, Heroes of Russia," and other top honorees. President Vladimir Putin personally addressed the audience and thanked them for their service.

From state media coverage of the event, St. Petersburg investigative journalist Denis Korotkov identified among the guests a man who he has been writing about for several years: Dmitry Utkin, who uses the nom de guerre "Vagner" and is believed to be the head of an unregistered private military contracting agency called ChVK Vagner.

Kremlin spokesman Dmitry Peskov on December 15 confirmed that Utkin, 46, was at the reception, adding that he qualified because he holds the Order of Courage. Asked why Utkin had been given the honor, Peskov only said: "Usually they give it for courage."

Korotkov and others who have been researching the shadowy world of Russian mercenaries see Utkin’s presence as the clearest indication yet of the key role paramilitary mercenary formations have played in Russian foreign policy for at least the last five years, particularly in Ukraine and Syria.

A tweet from Fontanka.ru, where journalist Denis Korotkov works, showing a photo of Utkin at the ceremony:

"Their function [in Syria] is very unclear," Korotkov told RFE/RL. "Based on how they are trained at their camp in Russia, it would seem to be preparation for special forces. That is -- for reconnaissance, work with diversionary groups, and things like that. Based on information coming out of Syria at first- or secondhand, the Vagner group is often used as elite infantry, which naturally leads to casualties much greater than special forces typically see. But who coordinates this work and who commands them, I don’t know."

It is a murky topic for many reasons, not least because mercenary activity is illegal in Russia. But by all indications, Russia has been using private military contractors in close cooperation with the military in ways similar to those pioneered by the United States in the early 2000s, particularly during the wars in Afghanistan and Iraq.

Using open-source material and contacts within Russian security structures, Korotkov has traced Utkin's career in detail. Prior to 2013, he was a brigade commander of the special forces of the GRU, Russia’s military intelligence service. Utkin retired in 2013 and began working for the Moran Security Group, a company founded by Russian military veterans that carries out security and training operations around the world, specializing in security against piracy. The same year, senior Moran managers were connected with the formation of a St. Petersburg-based organization called the Slavonic Corps, which advertised online looking for mercenaries to "protect oil fields and pipelines" in Syria.

A tweet by the Conflict Intelligence Team shows a photograph of men believed to be Vagner mercenaries in Syria:

According to various media reports, Utkin was given the sobriquet Vagner because of his affection for "the attributes and ideology" of Adolf Hitler’s Nazi regime.

The name ChVK (the Russian abbreviation for Private Military Company) Vagner first appeared in 2014, with reports that mercenaries from the group were fighting with Russia-backed separatists in eastern Ukraine. In 2015, reports indicated that they had moved back to Syria, and Korotkov published the first reports of Russian mercenaries on the ground in Syria and their recruitment in St. Petersburg just weeks after the beginning of Russian bombing raids there in October 2015.

The Vagner mercenaries reportedly played an important role in helping the forces of Syrian President Bashar al-Assad recapture Palmyra in May. Around the time that ancient city was captured, Korotkov said he received reports that several Vagner mercenaries had been given Russian military honors for fighting there, but he was unable to confirm them.

However, the Kremlin reception on December 9 seems to have provided at least some confirmation. The Rossia state television channel showed retired Colonel Andrei Troshev, a veteran of the Soviet war in Afghanistan who officially retired in 2014. At the time of his retirement, Troshev had not received the Hero of Russia medal, but he was clearly wearing one at the Kremlin reception.

Ruslan Leviyev, an analyst with the Conflict Intelligence Team project, first identified Vagner mercenaries from a video of killed "Russian soldiers" posted by the militant group Islamic State (IS) in Palmyra on March 17. His team also identified 51-year-old retired Major Sergei Chupov, who was reported killed in Syria on February 8, as a Vagner mercenary on the basis of interviews with his friends and relatives in St. Petersburg.

Leviyev said he is convinced the mercenaries are equipped and supported by the Russian Defense Ministry and its main intelligence directorate, known as the GRU.

"For one thing, their training ground is adjacent to the training ground of the GRU’s 10th Brigade [in the Krasnodar region]," he told RFE/RL. "If their existence was not approved by the government, then that would be impossible -- that they would be right next to an elite GRU special-forces base.

"Moreover, there are the photographs of the killed mercenaries that were published by IS -- you can see weapons that only elite GRU special-forces units have," Leviyev added. "We can also see on photographs posted [by mercenaries] that they are moving around Syria in Russian military aircraft. They are photographed next to Defense Ministry helicopters and airplanes. It is clear that they are getting help, transportation, and weapons from the government of Russia, from the Defense Ministry."

A tweet from the Conflict Intelligence Team shows photographs of weapons normally only used by elite GRU special-forces units that were shown in an Islamic State video:

Leviyev pointed out that the mercenaries in groups like Vagner are different from the unprofessional volunteer fighters who appeared in the early days of the conflict in eastern Ukraine.

"These are all people with considerable experience," he said. "As a rule, they are over 30 and have served in the military. There are some quite old people, like Sergei Chupov, who was 51. As a rule, these are not just some volunteers like we saw in Donbas, former miners or auto mechanics. These are people with real military experience serving in well-prepared military units."

Journalist Korotkov estimated that at least 600 mercenaries have fought with Vagner in Syria since 2014. He estimated as many as 60 have been killed there.

Leviyev said it is difficult to be precise on such numbers.

"The people we have spoken with who say they know people fighting with this mercenary group say that in the period of Russia's official involvement in Syria [since October 2015], several dozen of them have been killed," he told RFE/RL. "We have not been able to confirm this. As a rule, even those who are fighting as mercenaries have bereaved posts published by their relatives and friends, as was the case with Sergei Chupov. But we haven’t seen a flow of grief that would indicate dozens of dead."

The website militaryarms.ru reports that the Vagner forces are distinguished by "their very high percentage of losses, which is not characteristic of private military companies." The report says that in both Donbas and Syria, "Vagner mercenaries work in the most dangerous situations, often moving out in the first wave of an attack and storming population centers and enemy positions."

The appearance of Utkin and Troshev at the Kremlin function on December 9 raises another important issue, Leviyev says.

"I am not sure we can really use the word ‘mercenary’ in the sense that it is used in the Russian Criminal Code," Leviyev said. "As far as the military honors they have been given, from my point of view it is not possible to do that officially. They do get medals and this information is confirmed by various sources and some documents, but there are rules...and according to the rules it is not possible to give state medals to people fighting in such units on the territory of another country."

Russian officials last week acknowledged that 23 active military personnel had died in Syria since its bombing operations there began 14 months ago, according to state broadcaster RT.

RFE/RL Russian Service correspondents Andrei Sharogradsky and Mark Krutov contributed to this report