Last week's killing of more than 100 civilians at Houla in Syria may amount to crimes against humanity, the UN high commissioner for human rights has said.
Navi Pillay urged the international community to "make all efforts to end impunity" and "ensure accountability for perpetrators" of such "atrocities".
Pillay was addressing an emergency session of the UN Human Rights Council.
Earlier, opposition activists said there had been another mass killing of civilians by pro-government militiamen.
Anchor Aaron Schachter talks with Guardian correspondent Martin Chulov who has reported from the Middle East since 2005.