And in a video filmed nearby during the operation, Gen. Salim Idris, who leads the military council, is seen insisting that his forces played a leading role, in statements responding to criticism from Islamist groups that his fighters were hanging back. The report said it was unclear whether forces linked to General Idris took part in the initial Aug. 4 attack, when forensic evidence suggests most of the civilians were killed. But it also said that anyone continuing to coordinate with such groups could be complicit in war crimes.

The Human Rights Watch report accuses the five leading fighting groups of crimes against humanity; names several private donors in Kuwait and other Persian Gulf countries as financiers of the operation; blames Turkey for allowing the fighters to use its territory; and calls for an arms embargo against the five groups, adding to its previous calls for such an embargo against the Syrian government.

“Unified action by the international community is really long overdue when it comes to trying to deter these abuses and violations,” Ms. Fakih said, recommending that war crimes in Syria be referred to the International Criminal Court, which could investigate all parties.

The killings increased fear among the Alawite population, Syria’s largest religious minority. Alawites in the province of Latakia said in interviews that they were being indiscriminately targeted because President Bashar al-Assad and many government leaders are Alawites. During the attacks, an Alawite shrine was damaged and its sheik killed.

The report did not find evidence that children had been cooked in pots, fetuses ripped from mothers’ bodies or women sexually mutilated, as some government supporters had contended. But it documented several witness accounts of women, children and elderly people being gunned down as they tried to flee and of the infirm being killed in their homes, as well as forensic evidence that victims had been bound, decapitated or shot at close range.

In a school in Latakia converted into a shelter for people who had fled the villages, people indicated a willingness to speak of their experiences, but government officials prevented reporters from talking to anyone except Mr. Shakouhi, saying a psychiatrist had ruled that survivors were too traumatized to discuss the events.