International Criminal Court investigators arrived in Bangui on Thursday to begin probing the relentless violence that has plagued the Central African Republic for 18 months.
The ICC's first fact-finding mission since a preliminary probe was launched earlier this year comes amid unabated ethnic and religious violence that has prompted warnings that a possible genocide is imminent.
"Serious crimes have been committed since 2012 in Central Africa," ICC head of international cooperation Amadi Bah said at a news conference in the capital.
A coalition of mainly Muslim rebels launched an offensive in late 2012, eventually seizing power from president Francois Bozize in March last year.
Some of the fighters went rogue and the abuses they committed spurred majority Christians into creating vigilante groups, which have in turn carried out atrocities.
The daily looting, killing and raping raised global fears of a new Somalia-style "failed state" in the heart of Africa and sparked the launch in December 2013 of a military operation by former colonial power France.
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.
The ICC team will be investigating possible war crimes by members of both the officially disbanded Seleka rebel group and the so-called "anti-balaka" militias.
The ICC has already been investigating violence committed in Central Africa more than a decade ago by the former vice president of the neighbouring Democratic Republic of Congo, Jean-Pierre Bemba.
"Since 2002, investigations have been carried out and they are continuing in The Hague with respect to the 2002-2003 crimes," said Amadi Bah, the leader of the ICC tean in Bangui.
- Children burnt alive -
"Unfortunately, once again since 2012 serious crimes and unprecedented atrocities have taken place on Central African territory," he told reporters.
The ICC announced in February that it had opened an initial probe in the latest violence.
"My office has reviewed many reports detailing acts of extreme brutality... and allegations of serious crimes being committed," the court's chief prosecutor Fatou Bensouda said.
Her announcement came two days after a gruesome lynching that saw government soldiers stab, trample and pelt a suspected ex-rebel moments after a military ceremony attended by the new interim president.
Several other cases of lynchings and mutilation have been reported in recent months. Among the scores of people confirmed to have been killed this month were several children eyewitnesses said had been thrown alive onto fires.
Experts say such bloodshed is only the tip of the iceberg as foreign troops and the government's fledgling army have not reached some of the more remote part of the country.
The Central African Republic is a landlocked country larger than France that already ranked as one of the world's poorest before 2013 despite sitting on huge mineral deposits.
"They kill, loot, rape and steal with impunity. There is no one to protect the population from their abuses," Eric Ketegaza, a civilian fleeing a flare-up in the region of Mala this week, told AFP.
The Catholic Church has also been targeted by marauding gangs of gunmen and the medical charity Doctors Without Borders has had to scale down its operations after a deadly attack on one of its clinics.
The first Estonian contingent from a newly-deployed European peacekeeping force went on patrol in Bangui on Thursday, but foreign forces are struggling to make an impact.
The total number of foreign troops in the Central African Republic is expected to rise from its current level of around 8,000 to 12,000 late this year.