Internet video footage showing rebels in Syria carrying out summary executions in and around Aleppo, has prompted an outcry from governments and human rights groups.
One video shows four men identified as members of the pro-Assad Shabbiha militia being led down a flight of stairs and shot in a hail of gun fire, Reuters reports.
Russia's Deputy Foreign Minister Gennady Gatilov says the killings confirm human rights violations are taking place on both sides.
Human Rights Watch says the act was potentially a war crime and the opposition Syrian National Congress has condemned the killings.
Earlier, an Amnesty International report said government forces had also committed crimes against humanity in Aleppo, indicating that killings of prisoners and unarmed civilians were being carried out by all sides in the civil war.