A mass grave containing at least 26 human skeletons discovered in Germany shows that conflict in Neolithic Europe some 7,000 years ago could be horrifically brutal, with victims tortured and mutilated, reports a new scientific study.

The discovery adds fresh evidence to the theory that mass violence played a crucial role at the beginning of the Neolithic era, and might have contributed to the decline of the so-called Linear Pottery culture, said the study, published Monday in the Proceedings of the National Academy of Sciences of the US.

The significance of such ancient mass graves -? which remain rare -- has been hotly debated by experts.

The last one was found in 2006 in Germany during a road construction project.

Evidence to date suggests that "massacres of entire communities were not isolated occurrences but rather were frequent features of the last phases" of the Linear Pottery culture, the authors conclude.

Analysis of the 26 people in the grave indicate that the victims had not been buried with typical funeral rites.

Rather, the skulls of many of the skeletons were smashed in by violent blows, in addition to arrow injuries that may have killed or immobilized the victims.

Unique to the new site is the discovery of skeletons with significant trauma in their lower legs, indicating they were tortured or mutilated before after death, researchers said.

The study speculates that a clash over resources, possibly exacerbated by drought, could have sparked conflict between groups.