Former President Laurent Gbagbo is awaiting trial at the International Criminal Court on charges he committed crimes against humanity during a post-election crisis in Ivory Coast in 2010. The fallout from the election pushed the country to the brink of civil war.
Human rights groups have said both sides likely committed atrocities during the conflict.
Human Rights Watch said eight people were killed in April by Liberian and Ivorian rebels who fought alongside fighters loyal to Gbagbo. Rebels said they remained loyal to forces fighting in opposition to Ivorian President Alassane Ouattara.
Matt Wells, a specialist in West African affairs for the organization, said Liberian authorities weren't living up to their responsibility in terms of the regional conflict.
"Rather than uphold its responsibility to prosecute or extradite those involved in international crimes, Liberian authorities have stood by as many of these same people recruit child soldiers and carry out deadly cross-border attacks," he said in a statement from Kenya.
Human Rights Watch said it documented children as young as 14 years old at training camps along the Liberian border with Ivory Coast.
Gbagbo was arrested in April 2011. Human Rights Watch said many of the Liberian mercenaries who supported him have remained in Ivory Coast.