The International Criminal Court (ICC) has opened a formal investigation into an "endless list" of atrocities committed in the Central African Republic, prosecutor Fatou Bensouda has said.
"My office has gathered and scrupulously analysed relevant information from multiple reliable sources," Bensouda said in a statement on Wednesday.
"Based on this independent and comprehensive analysis, I have concluded that an investigation is warranted."
The move comes after a preliminary ICC investigation earlier this year into the violence that has plagued the country for more than 18 months established that there were grounds to prosecute war crimes and crimes against humanity.
The country was plunged into conflict after a coup in March 2013, led by a coalition of rebels known as Seleka, which overthrew president Francois Bozize and made their own man, Michel Djotodia, head of state.
Influential foreign leaders in January forced Djotodia to step down after he proved incapable of preventing widespread atrocities by rogue Seleka fighters.
Communities from Central Africa's mainly Christian majority responded by setting up vigilante forces known as "anti-balaka" (loosely translated as anti-machete) to seek vengeance, mostly targeting Muslim civilians whom they accused of backing Seleka.
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Bensouda said there was "a reasonable basis to believe that both the Seleka and the anti-balaka groups have committed crimes against humanity and war crimes."
They could include murder, rape, forced displacement, persecution and using child soldiers, she said.
"The list of atrocities is endless," Bensouda said. "I cannot ignore these alleged crimes.
"My office will now work to directly collect criminal evidence with a view to identifying and prosecuting those responsible for the most serious crimes."
New UN mission
Thousands have been killed and around a quarter of the country's 4.6 million people displaced since the start of the fighting in the Central African Republic.
"An impartial enquiry to identify those responsible for the most serious crimes from all parties is crucial to bring justice to the victims and send a clear signal to all perpetrators that they may be held to account," Richard Dicker of Human Rights Watch said.
"We look to the international community and the CAR authorities to lend their full support and cooperation to this investigation," Dicker, the head of HRW's international justice programme, said in an email to the AFP news agency.
"Mass crimes shock the conscience of humanity and tear at the social fabric of society," said Bensouda.
A new UN mission took charge of peacekeeping operations in the Central African Republic last week, tasked with ending ethnic and religious bloodshed and restoring stability. It will eventually consist of 12,000 soldiers and police officers.