Prosecutors in the Central African Republic (CAR) on Thursday announced a probe into suspected war crimes and crimes against humanity after more than two dozen people were massacred last month.
The inquiry will focus on events in the northeastern town of Ndele on April 29, chief prosecutor Eric Didier Tambo told AFP.
"We have recorded around 30 bodies, including a mother and her baby," Tambo said.
"We conclude that... war crimes and crimes against humanity occurred."
He added: "As these are armed groups which attacked civilians, their leaders are the chief suspects."
He said that he visited Ndele to investigate the violence of April 29 and clashes that broke out there on March 11.
According to the UN peacekeeping mission MINUSCA, 28 people were killed, of whom at least 21 were civilians, on April 29. At least 13 people were killed on March 11.
The violence opposes two groups from the Popular Front for the Rebirth of the CAR (FPRC), one of the country's biggest militias.
One group is drawn mainly from the Runga ethnic community, while the other "comprises only ethnic Gula" members, said Tambo.
Once comrades in arms, the two groups are fighting for control of the region's rich diamond deposits and lucrative income from road blocks.
One of the world's poorest and most unstable nations, the former French colony has suffered several crises since 2003 when former president Francois Bozize seized power in a coup.
The country spiralled further into bloodshed after Bozize was overthrown in 2013 by the mainly Muslim rebel Seleka alliance.
The government signed a peace deal in February 2019 with 14 armed groups, who typically claim to defend the interests of specific communities or religions.
Violence has since generally receded, but there are still bloody flareups and more than two-thirds of the country remains under militia control.
Tensions between the Gula and Runga first spilled over last September in the town of Birao on the Sudanese border and then again in Bria, a diamond centre in the east of the country, in January.
MINUSCA on Wednesday defended itself against accusations that it had been slow to respond to the violence on April 29.
"MINUSCA members were at (Ndele) market in less than 30 minutes and repelled the attackers," spokesman Vladimir Monteiro said.
"The situation was extremely complex, with local people fleeing and shots fired by combatants in civilian clothes who could not be identified."
Additional UN forces have been sent to the town, he said.