Syrian rebels executed some 30 captured government soldiers last month, UN rights chief Navi Pillay said Friday and called for an investigation into the alleged massacre, dpa reported.
The execution-style killings took place in Khan al-Assal, a town near Aleppo, the UN High Commissioner for Human Rights said in a statement.
"Based on the analysis by my team to date, we believe armed opposition groups in one incident - documented by a video - executed at least 30 individuals, the majority of whom appeared to be soldiers," Pillay added, calling the killings "deeply shocking."
Rebels posted several online videos last week showing people who had died in the incident.
Pillay's office documents massacres and other human rights violations in Syria.
Khan al-Assal is also one of the three sites that UN inspectors want to visit to investigate alleged use of chemical weapons.
The government and rebels blame each other for a purported chemical attack on March 19 that killed at least 30 people there.