United Nations monitors have found human remains in a Syrian village, where it is claimed 78 people were massacred.
They also discovered evidence that government troops had been in Mazraat al-Qubeir.
Syrian authorities have blamed terrorists for the killings, which are said to have happened on Wednesday.
The alleged massacre and continuing violence elsewhere demonstrate how little outside powers have been able to do stop the fighting, which is becoming increasingly sectarian.
UN chief Ban Ki-moon has warned there is an imminent threat of full-scale civil war in Syria.