Human Rights Watch says soldiers from the Republic of Congo killed at least 18 people while serving as United Nations and African Union peacekeepers in Central African Republic more than a year ago.

The rights group said Tuesday that the Republic of Congo has not set up credible investigations into the killings, and it urged action to make the soldiers accountable. Troop-contributing countries to AU and U.N. peacekeeping missions are responsible for prosecuting alleged crimes by their troops.

The organization said the exhumation of a grave in February uncovered remains of 12 people who peacekeepers said had escaped after being detained in March 2014. The group also documented death by torture of two Christian militia leaders, a public execution of suspected militia members and the deadly beating of two civilians.