Many LRA fighters are abducted children
Uganda's rebel Lord's Resistance Army is continuing to carry out attacks in the Democratic Republic of Congo, says the UN refugee agency.
Rebels attacked a village this week, killing four people, including a girl of four and abducting a boy of nine, locals told the UNHCR.
A bishop in South Sudan says two men had their hand and legs chopped off and were beaten to death, as boys watched.
The LRA now operates in at least four countries in the region.
The government of the CAR has sent troops to its border with DR Congo in an effort to push back the rebels, the country's defence minister said on Wednesday.
A team from the UNHCR has reached Duru, a once vibrant Congolese village that is now deserted.
The survivors of the LRA attacks told the UN agency that the rebels looted and torched their houses, forcing them to flee into the forest.
"What we saw was shocking," David Nthengwe, UNHCR spokesman for eastern DR Congo, told the BBC.
"People live in fear in the forest. Many of them are unable to move, as they fear that the LRA is going to attack them."
He said people had gone for days with no food, sanitation or medical assistance and were in desperate need of water and other basic supplies.
But he said the poor security situation has prevented humanitarian aid workers from reaching them.
The BBC has also received accounts from the Anglican church in the Sudanese diocese of Mundri of other atrocities.
Bishop Bismark Avokaya says that LRA rebels abducted two 10-year-old boys.
Two of his parishioners then followed the rebels to try to rescue them but they were caught.
Their hands and legs were hacked off while they were both alive, and they were then beaten to death in front of the boys who have now been rescued.
"Both are traumatised like many others and we could not believe our ears as they shared the stories with us," the bishop said.
LRA leader Joseph Kony refused to sign a peace deal last year until International Criminal Court arrest warrants are withdrawn.
Ugandan, Congolese and Sudanese government forces then carried out a joint offensive against the rebel positions.
But since Christmas Day, suspected LRA rebels have been attacking villages across hundreds of kilometres in an area stretching from the Central African Republic (CAR) though Sudan and into DR Congo.
More than 500 people have been killed and over 100,000 have fled from their homes to escape the attacks.
The LRA have been fighting in northern Uganda for two decades but are now based in DR Congo.