At least 400 have fled over the border into Congo.
Congo, too, has suffered attacks, the world body's refugee agency says. In February, the Lord's Resistance Army killed as many as 100 people there.
The agency said Tuesday the attacks in Central African Republic this spring were marked by an increase in brutality.
The LRA began its attacks in northern Uganda more than 20 years ago and has since spread to Congo, Sudan and Central African Republic. It has no known agenda except killing and kidnapping to swell its ranks.