The bodies of 29 Mauritanians and four Malians were found near the village of Robinet El Ataye in the Segou region, where 33 civilians had been beaten and taken away on March 5, the UN Group of Experts on Mali said in a report to the Security Council late last month.
A diplomatic source in New York told AFP that the white soldiers were paramilitaries of Russia's Wagner group.
Mali hired the mercenaries to back up its military junta, while at the same time driving out French forces that had provided assistance in addressing Islamic jihadists and other insurgents.
Mali has also worked against the UN MINUSMA security force operating in that Sahel nation, halting troop rotations for that unit.
Wagner is well known for its operations in Mali, the Central African Republic, and now, reportedly, Ukraine, where Moscow is using Wagner gunslingers to supplement its depleting forces facing Ukrainians seeking to repel Russian invaders.
A number of rights groups and NGOs have accused Wagner Group of gross human rights violations and crimes against humanity.