NAIROBI, Kenya - A rights group says a Ugandan rebel group known for committing atrocities has killed at least 255 adults and children in the past 18 months in Congo and Central African Republic.

Human Rights Watch says in a report released in the U.S. on Wednesday that the Lord's Resistance Army killed the victims after they tried to escape, walked too slowly, or were unable to bear the heavy loads they were forced to carry.

The group said the killed were part of almost 700 adults and children abducted in the two countries.

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.