The UN says more than 140,000 people fled their homes in the Haut-Uele district in the wake of what the report calls the "Christmas massacres" beginning on Christmas Eve.
The attacks by rebels of Uganda's Lord's Resistance Army (LRA) followed a co-ordinated offensive against them by troops of Uganda, DR Congo and South Sudan.
That night I heard the LRA celebrating. Then they slept there among the bodies of those they had killed
In some of the worst cases, LRA rebels waited until people had gathered for Christmas celebrations and then hacked victims to death with machetes and axes or crushed their skulls with clubs and heavy sticks.
One elderly man told Human Rights Watch (HRW) how after arriving late for Christmas lunch at a hamlet in the Doruma area, he hid in bushes while LRA rebels killed at least 82 people.
"When they finished I slipped away and went to my home, where I sat trembling all night. That night I heard the LRA celebrating. Then they slept there among the bodies of those they had killed," he said.
The HRW report accuses military planners of failing to make adequate preparations to protect civilians from reprisals, and said Congolese soldiers had only arrived in some of the affected areas - like Doruma and Faradje - after the attacks.
"We're seeing very little protection of civilians there. We have less than 300 UN peacekeepers in a humungous area, this is something like 15,000 sq km," Anneke van Woudenberg, a senior HRW researcher, told the BBC.
"Almost no UN peacekeepers are there. And of course the Ugandans and the Congolese who are involved in an operation against the LRA are not doing nearly enough to protect the civilians," she said.
She said an additional 3,000 troops authorised for DR Congo by the Security Council had not yet materialised.
Countries from Uganda to the Central African Republic have suffered 20 years of terror inflicted by the LRA and tens of thousands of children have been abducted to be fighters and sex slaves.
LORD'S RESISTANCE ARMY ATTACKS DECEMBER 2007 - JANUARY 2009
Number of villages attacked: 74
Attacked once: 47 Attacked twice: 9
Attacked three times: 5 Attacked eight times: 1 (Duru)
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