Moscow -- Three Russian journalists have been killed in Central African Republic while investigating a secretive Russian military contractor.

Two of the journalists were among Russia’s most respected: Orkhan Dzhemal, a veteran war correspondent, and Alexander Rastorguyev, a leading documentary-maker. Their cameraman, Kirill Radchenko, regarded as a promising young videographer, was also killed.

Local authorities have said the men were killed on Monday night when their car was attacked in an ambush by unknown gunmen, who may have been local militants. The three journalists' bodies were found by troops from a United Nations peacekeeping force on Tuesday, around 120 miles from the capital, Bangui. Russia's foreign ministry has said preparations are being made for the bodies to be returned.

The journalists were in the country making a documentary in partnership with a Russian news organization called the Center for Investigation (TsUR), that is funded by the exiled Russian oligarch Mikhail Khodorkovsky. On Tuesday, the organization said the documentary was examining the activities in the Central African Republic by the so-called Wagner Group, a Russian private military contractor.

The Wagner Group is a mercenary force that has been fighting recently in a number of conflicts around the world where Russia is involved. The company supports pro-Kremlin forces, most prominently in eastern Ukraine and in Syria. It has been tied to Evgeny Prigozhin, a business mogul often nicknamed “Putin’s Chef” who was indicted by the U.S. special counsel Robert Mueller for his role in U.S. election interference by Russia. Many experts believe that the Kremlin tasks Wagner with military operations where it is unwilling to deploy regular Russian troops publicly.

In the past year reports have emerged that Wagner is operating in Central African Republic, providing security and training to the war-ravaged country’s government. The Central African Republic (CAR) is in the grip of a chaotic 15-year civil war between multiple rebel groups and its current internationally-recognized government, headed by President Faustin-Archange Touadéra. Most of the country is beyond the government's control and 12,000 UN troops are battling to contain the chaos.

Russia has recently become involved in supporting Touadéra's government, supplying arms deliveries and training the government's security forces after receiving UN permission.

In April, the French newspaper Le Monde first reported the presence of the Russian mercenaries in CAR, noting that Russian-speaking men in military fatigues but without insignia were acting as bodyguards for Touadéra. The French news agency AFP reported that the Russians had established a military camp in Berengo in a ruined palace of the country's former dictator and were training government forces. Le Monde identified the mercenaries as working for two companies, Sewa Security Services and Lobaye Ltd., which Russian investigative media has suggested are in fact controlled by the Wagner group.

Responding to the reports, Russia's foreign ministry said that as part of its UN-authorized efforts to assist Touadéra's government, five military instructors and 170 "civilian instructors from Russia" had been sent to CAR to help train its security forces.

On Tuesday, the Center for Investigation’s deputy editor-in-chief, Anastasia Gorshakov, told TV Rain that the three men had tried to enter the Russian base at Berengo on Sunday but were turned away after they were told they needed accreditation from CAR’s defense ministry. The men were told they might receive accreditation in five days’ time, she said. The men were killed as they tried to travel to another town to meet with a fixer, she said.

The purpose of the the three journalists' trip has swiftly prompted some speculation in Russia that they may have been killed for their efforts to investigate Wagner, which has a reputation for exceptional secrecy. Some speculated that the journalists could have been investigating possible illegal deals between the mercenaries and local rebel groups around conflict diamond mining.

On Tuesday, the spokeswoman for Russia’s foreign ministry said allegations that the killings could be connected to the men's investigation were “drivel.”

"Judging by where the bodies were found, the Russian journalists were not heading for the area of the instructors' deployment," the spokeswoman Maria Zakharova wrote in a statement, adding that it appeared the men had ignored a warning not to leave the area controlled by local law enforcement.

“It is still a question what they were actually doing in the Central African Republic and what their agenda was," she said.

Referring to reports around the Wagner mercenaries, she responded, ”There is nothing sensational about the presence of Russian instructors in the Central African Republic, no one has been concealing anything."

Russia's Investigative Committee, the equivalent of the FBI, said it was opening a criminal case on the killings.

Suspicions about Wagner’s relationship to the Russian government were underscored by Russian state media reports. The reports on Tuesday included no mention of Wagner, instead noting that the three men were making a documentary “about life in the Central African Republic.”

Local authorities in CAR, however, have so far suggested the men were likely victims of a straightforward highway robbery. Marcelin Yoyo, an official in the town of Sibut where the men had been, told The Associated Press they were attacked about 14 miles away from their last known location.

Yoyo said the men’s driver survived the attack and managed to flee and report the ambush. According to the driver, the attack was carried out by armed men “all turbaned and speaking only Arabic.”

Yoyo told the AP that security forces had warned the group not to go because it was late and they could meet militant fighters.

On Tuesday, the Russian state news agency TASS said there were reports the journalists had been attacked by members of the Seleko, a coalition of Muslim rebel groups that are at war with the country’s government.

The killings deprive Russia of some of its most highly-regarded and intrepid reporters. Dzhemal was known as a fearless war correspondent who had covered many of the world's major conflicts of the past two decades, from Chechnya and Ukraine to Syria and Libya's civil war. Rastorguyev was considered one of Russia's most radical documentary directors, one of a small group of filmmakers known for tackling risky political and social subjects. His most recent film had followed the Kremlin's leading political opponent, Alexey Navalny.