BANGUI, Central African Republic (AP) — Authorities in Central African Republic have opened an investigation after a low-flying fighter jet dropped explosives near a base for Russian mercenaries working with the country's military.

The attack took place in the early hours of Monday at the Cotenaf base in Bossangoa, where witnesses said both the base used by Russia's Wagner Group and surrounding homes had been hit.

"The Russian paramilitaries showed their indignation very early by shooting in the air from 5 to 6 o’clock. For the moment the city is quiet, the shops are not yet open and people are afraid to go about their business,” said Robert Faradanga, a local community journalist.

It was not immediately clear who was responsible for the aircraft that dropped the explosives.

Information Minister Serge Ghislain Djorie said in a statement that the unknown aircraft headed north after the incident before leaving the country's airspace.

“This despicable act perpetrated by the enemies of peace will not go unpunished,” Djorie said.

In Central African Republic, Wagner fighters ride around the capital Bangui in unmarked military vehicles and guard the country’s gold and diamond mines. They have helped to hold off armed rebel groups and to keep President Faustin-Archange Touadera in power.

However, the mercenary group also has been accused of committing human rights violations. A report released earlier this year by the U.N.'s independent expert on the human rights situation in Central African Republic cited a number of attacks it said were reportedly carried out on the orders of the country’s armed forces and their Wagner Group allies.

In one instance, Russian mercenaries prevented U.N. peacekeepers from accessing a village where the country’s armed forces and the Russians had “reportedly opened fire on civilians indiscriminately.”

In one of the attacks reportedly ordered by the Russians, militants went to the village of Boyo and killed 19 male civilians. The report by Yao Agbetse, the U.N.’s independent expert, also stated that wounded people had been buried alive.

Associated Press writer Krista Larson in Dakar, Senegal contributed.