Moscow (CNN) The oligarch whose company is linked to the Russian mercenary group believed to be behind an attack on US and allied forces in Syria earlier this month is alleged to have made a systematic effort to silence reports of his activities, CNN has learned.

Russians who have come into the orbit of Yevgeny Prigozhin -- the man dubbed "Putin's chef" by the local press -- have told CNN of being pursued on social media and confronted in person after making critical comments or asking probing questions.

Prigozhin has been at the center of the confrontation between Washington and Moscow. He was indicted last week by the US special counsel, and the US claims his business empire has effectively become an arm of Russian foreign policy. US investigators believe he financed a Russian " troll factory " that spread fake news during the 2016 US presidential campaign. He is also believed to be linked to Wagner, a mercenary firm involved in a deadly encounter with US forces and their allies in Syria on February 7. His company has denied allegations of a link to Wagner.

US investigators believe Prigozhin is the same man who bankrolled the Internet Research Agency, a company that the US indictment says created fake online personas to wreak havoc with the US political system, including the 2016 elections. Prigozhin told Russian state news agency RIA Novosti that he's not concerned about the indictment. "I'm not at all upset that I'm on this list," he said. "If they want to see the devil, let them see one."

Russians tracking the activities of Prigozhin say they see a pattern of harassment and intimidation.

Yevgeny Shabaev, who has spoken in Russian-language media on behalf of mercenaries wounded in the attack and who says he has visited some of the wounded, said he had received a message warning him against publicizing Wagner casualties. The message appeared to be linked to a fake social-media account that had no photos.

"He will fight like a trapped beast, if necessary," the message, seen by CNN, to Shabaev read. "A couple of weeks ago, this beast had suffered major losses, but this just makes him angrier, and his group of professional annihilators didn't go anywhere. So decide for yourself if it¹s worth teasing this beast even more."

It was not possible to confirm that the message originated with Prigozhin's network of companies; CNN made repeated efforts to reach Prigozhin's representatives for comment. Shabaev speculated that he was being warned by the oligarch or those sympathetic to him.

Shabaev is an ataman, or leader, of the Khovrino Cossack Society, a conservative paramilitary organization that has provided volunteers to fight in Syria as well as in eastern Ukraine, where pro-Kremlin separatists have been fighting the Ukrainian government. Shabaev said friends had informed him about phone calls they received from unnamed callers looking for kompromat (compromising information) about him.

The Washington Post reported Thursday that Prigozhin was "in close touch" with Russian and Syrian officials ahead of the clash with US and allied troops, raising new questions about the depth of Prigozhin's involvement in Russia's war in Syria. The Russian government has never openly acknowledged that it has mercenaries fighting in Syria, and has been reluctant to confirm Russian casualties in the clash with US-backed forces.

Earlier this week, the Russian Foreign Ministry said "several dozen" Russians were injured and an unspecified number killed in the incident, which occurred after a large force of Russian contractors and Syrian pro-regime forces approached a base of the US-backed Syrian Democratic Forces near Deir Ezzor. An American detachment was at the base, and the US responded with airstrikes that killed around 100 attackers, according to the coalition.

The Foreign Ministry initially played down reports of major losses, saying only that possibly five people died. The deadly incident was also a story the reclusive tycoon appears eager to suppress: Shabaev speculated Prigozhin's representatives have made efforts to bury the story about massive casualties among the Russian soldiers-for-hire.

Russian investigative reports say Wagner contractors sign nondisclosure agreements as part of their employment. And Russian journalists tracking Prigozhin say they have also received indirect threats they believe are being made by individuals affiliated with or sympathizing with Prigozhin.

Denis Korotkov, an investigative reporter at the independent media outlet Fontanka, said threats didn't come directly to him, but rather through his friends and colleagues on social media, as Korotkov has no social-media profile of his own. Korotkov said his friends received messages from fake accounts asking for his personal details and address, claiming they were his classmates and wanted to send him a gift. Fontanka researchers were able to track the IP addresses to Glavset, a legal entity associated with the Internet Research Agency.

Negative comments about Fontanka also flooded the web. In essence, the troll factory was trolling its critics, Korotkov and others believe.

"Google 'Denis Korotkov is a traitor' -- you¹ll get hundreds and hundreds of links saying that," he said. "The text is all the same. What am I supposed to do, cry? I¹m a grown man. It¹s part of the job."

CNN has viewed anonymous online comments deriding Korotkov and his colleagues as traitors. But the threats have not been limited to online harassment. Local activists in St. Petersburg also have described physical assaults and attacks they believe are carried out by individuals affiliated with or sympathetic to Prigozhin.

Danila Aleksandrov reported that he was hit in the face six times as he was walking out of his house in February 2016. A few days before the incident, a friend of his said in a Facebook post that Aleksandrov received a threat from what appeared to be a fake account on VKontakte, a popular Russian social media site. The post included a picture of Aleksandrov, secretly filmed while walking his dog.

In a post on Facebook, Russian internet researcher Lyudmila Savchuk, who managed to penetrate the troll farm as part of an investigation, warned that Prigozhin and his allies would retaliate.

"Dear colleagues, when you are preparing materials about Prigozhin and the troll factory now, do not forget, please, that in addition to these crimes, people associated with the troll factory have committed a series of attacks on opposition bloggers in St. Petersburg," she said. "The criminals got away without any punishment."

One former troll agrees: Marat Mindiyarov, who previously worked at the so-called troll factory, said he was also the target of recent retaliation after going public about his experience. Early this week, he was detained for five hours by police in St. Petersburg investigating an apparent bomb threat. He was released without charge.

"I think there is some link" between interviews he gave to media about the troll factory and the arrest, Mindiyarov speculated. "I think they don't want me to talk about it, because it was the factory of lying."