The United Nations office of humanitarian affairs on Friday said it had credible reports about the slaughter on Thursday at a camp near Gulu.
The attack was carried out by rebels belonging to the Lord's Resistance Army (LRA), it said.
The UN agency estimated that more than 200 huts were burned by the rebels and some 7000 people left homeless.
"These attacks against some of the most vulnerable civilians in the world are an outrage," said Jan Egeland, the UN emergency relief coordinator.
LRA, an eccentric Christian group with no clear objectives except to discredit President Yoweri Museveni, has abducted thousands of children since 1997 and forced them to serve as fighters, porters and sex slaves in camps in Sudan.
Some 1.5 million people have fled the fighting between government troops and the rebels. Many now live in 60 squalid camps, set up in the remote north of the country.
In February, the LRA rebels had shot, clubbed and burned to death 200 people during an attack at a camp near the town of Lira.
LRA, led by self-proclaimed prophet Joseph Kony, has become notorious for its brutality, often slicing off the lips and ears of its victims.
Kony and some of his associates are being investigated by the new International Criminal Court for war crimes.