By Tim Lister, Clarissa Ward and Sebastian Shukla, CNN

(CNN) -- A new investigation has found evidence that CNN journalists in the Central African Republic (CAR) last year were subject to constant surveillance by a team of Russian operatives.

Bellingcat -- an investigative website that researches illicit Russian activities abroad -- has concluded that when a CNN team landed in the capital Bangui in May 2019 to investigate Kremlin-linked operations in the country, "plans had already been put in motion for their surveillance, intimidation, and ultimately attempted discrediting."

Those plans involved people associated with Russian oligarch Yevgeny Prigozhin, whose military contractors were in the CAR training new elements of a national army, and whose companies had lucrative mining concessions there.

The CNN team had reported extensively on Prigozhin's activities -- including his links to Wagner, a private military contractor, and the Internet Research Agency (IRA). Prigozhin was sanctioned by the United States in 2019 after the Treasury Department said he had funded the IRA, an internet troll factory, in an attempt to influence the 2018 US midterm elections.

CNN had also reported on Prigozhin's growing interests in Africa, and the unexplained murders in 2018 of three Russian journalists investigating the activities of Russian mercenaries in the CAR.

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Bellingcat obtained a memo it said was circulated among Russian team-leaders in the CAR, including political strategists and security contractors. Distributed the day before the CNN team flew in, it said: "The assignment is to monitor the journalists 24 hours a day, 7 days a week, for the purpose of being promptly informed of their movements and meetings."

The memo detailed the methods of surveillance, which included "non-stop undercover surveillance" using multiple cameras, including two "camouflaged as pens." It also said that some involved in the operation "must be wearing clothes that allow them to enter the hotel and stay for a short time in a restaurant or a bar."

According to Bellingcat, the operation was run by a company based in St. Petersburg called Convoy Military Security, which is directed by a man called Colonel Konstantin Pikalov. Bellingcat says Pikalov was the liaison between Russia's Ministry of Defense and Prigozhin's political, media, and mining operations in Africa.

The Bellingcat investigation says that according to email correspondence from Prigozhin's employees, "Konstantin Pikalov was also the author of the surveillance memo targeting the CNN team."

The CNN team, led by Chief International Correspondent Clarissa Ward, encountered a man closely resembling Pikalov at a dinner in Bangui, but he was not conclusively identified.

Throughout the CNN team's stay in the CAR, there were indications that their movements were being tracked. On the first day of filming, two men on mopeds followed CNN's vehicle, then sped off when confronted.

Later, two men posing as local journalists asked Ward for an interview at the hotel. It later transpired that they were working for the Russians; the meeting was featured in a video released by the news agency owned by Prigozhin, RIA/FAN, in August 2019.

The surveillance and harassment intensified on a second visit to the CAR. Ward planned to visit diamond mines where a Prigozhin company -- Lobaye Invest -- had been granted generous concessions.

A man who had offered his assistance on the first trip was in the hotel lobby in Bangui, taking photographs of Ward. He was later seen in a restricted airport area when the CNN team was about to fly to a town called Boda.

The diamond mines are in a very remote area of the CAR, several hours' drive over rough tracks from Boda. But the surveillance and harassment continued there. Local police questioned the CNN team, accusing them of faking a press accreditation.

More disturbing was a vehicle with several white passengers that was trailing CNN's team. When Ward approached the car it drove off at full speed, with most of its occupants hiding their faces. However, it reappeared later near Boda. The mayor of the town told CNN that the same vehicle had been spotted near the local airfield overnight, with the foreigners apparently sleeping in the car.

CNN was able to confirm the identity of one of the men in the car: Klim Kasyanov, from St. Petersburg. Bellingcat has established that Kasyanov was with a group of Russians -- primarily from media controlled by Prigozhin -- in the CAR in 2018, soon after the Russian journalists were murdered on a remote road.

At least some of the Russian surveillance of CNN's team ended up in a slickly produced video released in August 2019 by RIA/FAN. The video included claims that the CNN team was linked to US and UK intelligence services and included multiple examples of the video and photo surveillance of the CNN team.

It claimed the two locals who had met Ward at the hotel were offered cash to lie about adverse experiences with Russians. It even included video from inside Ward's hotel room.

Speaking on CNN two days after the publication of the smear piece by RIA FAN, Ward said "on one level it is sinister and frightening, but on another level it is somewhat satisfying. It makes it clear our reporting has hit a nerve and that we are telling a story that some people would rather not see told."

Bellingcat concludes that "there's little doubt that the surveillance, intimidation and defamation campaign against CNN in the CAR could not have been executed by Yevgeny Prigozhin's private organization alone (sic) without the collaboration of the Russian state via its official military presence" in the CAR.

In its previous reporting, CNN has made repeated efforts to obtain responses from Prigozhin and parts of his business empire -- without success.

But CNN is far from the only target for Prigozhin's associates, who have also sought to discredit and harass local Russian media and the New York Times. "The active measures employed against CNN follows a long-established modus operandi used by Prigozhin's private operations against journalists whom he perceives as threats to his -- and the Kremlin's -- interests," the Bellingcat report found.

Bellingcat says the modus operandi is consistent: a "combination of unlawful surveillance, private intimidation, public discrediting, and endangerment via spreading of false information that might make the journalist a target of attacks by third parties."