A local unit of the French wine, beer and soft drink group is suspected of having made payments to local militia, the source said.
A spokesman for Groupe Castel said the company was fully cooperating with French authorities on the matter, and that an internal investigation following the first accusations had shown no evidence of wrongdoing.
Non-governmental organisation The Sentry earlier said the probe had been launched after it submitted a report detailing how a subsidiary of Groupe Castel, SUCAF RCA, may have made payments to the militia groups responsible for torture, rape, and mass killings.
Groupe Castel runs a sugar operation in the CAR, a country that has been racked by violent conflicts for years.
The source close to the matter said the probe that opened in Paris did not formally target the group or executives, but had been opened “against X”, which allows prosecutors to investigate in all directions.
With the launch of the investigation, The Sentry’s lawyers Clemence Witt and Anaïs Sarron told Reuters the prosecutor’s office would now be able to hear witnesses and order searches and seizures.
“The facts are being investigated under the legal qualification of complicity in crimes against humanity and war crimes committed by armed militias in the Central African Republic,” they said.
“The prosecutor’s office will now launch its investigations in order to establish the truth.”
(Reporting by Sarah Morland, editing by Tassilo Hummel and Gareth Jones)