A grave containing "numerous" bodies allegedly killed by rebels has been found in north-eastern Democratic Republic of Congo, UN peacekeepers say.
Jerome Kakwavu's commanders deny committing human rights abuses
An underground jail had also been found in a "torture camp" run by the FAPC rebels, said a UN spokesman.
The rebel-run Ndrele camp was on Sunday the scene of clashes between the rebels and the UN after peacekeepers tried to investigate reports of abuses.
A senior FAPC commander denied the claims, saying camp inmates were free.
Ndrele camp is about 20km from the Ugandan border, close to the town of Mahagi in Ituri province, which has been riven by fighting between rival militia groups.
The BBC's Mark Doyle, who has just visited Ituri, says there are at least seven militia groups there, which are formed along ethnic lines and present themselves as self-defence groups for their communities.
But he says their real purpose is to extract economic rent on behalf of the warlords who control them.
The FAPC, headed by Major General Jerome Kakwavu, has long controlled a key gold mine in mineral-rich Ituri.
A spokesman for the UN mission in DR Congo (Monuc) said after being denied access to Ndrele on Sunday, the UN troops launched an attack in which two FAPC militiamen were killed.
Several Monuc troops were injured but are now safe.
Monuc spokesman Mamadou Bah says there is no doubt that the FAPC forces have been carrying out human rights violations in the area under its control.
"They were looting, killing and raping children," he said.
FAPC's chief of operations Colonel Didier Wanican, currently in Kampala, vehemently denies that his militia has carried out any human rights abuses.
"This is not true. We are giving security to the people," he said.
"They are free to do what they want. They are the ones who asked us to be there."
The BBC's Will Ross in Kampala says this claim of popularity contrasts greatly with Monuc's reports that following the operation in Ndrele on Sunday, the local population has celebrated as the militia fled and has welcomed the arrival of the blue helmet troops of the UN.
Mamadou Bah said the operation serves as a warning for leaders of other armed groups - such as Thomas Lubanga of the Union of Congolese Patriots (UPC) - which the Monuc spokesman said has been harassing the UN operations.
Although Monuc says it has now liberated Ndrele, the problem is clearly not solved as the militia has now scattered - the guns are still out there, our correspondent says.
Colonel Wanichan claims the FAPC troops are willing to disarm and join the national army but he blamed the Kinshasa government for acting slowly.
However, Monuc's Mamadou Blah reports that militia including the FAPC have been sabotaging the disarmament process.
"These Ituri warlords have even conducted violence against men who wanted to disarm voluntarily."
Mamadou Bah urged the Kinshasa government to offer positions to the warlords in the transitional government.
Disarming and forming a national army is one of the key challenges for DR Congo where elections are optimistically due to be held in six months' time.