In a coordinated attack, numerous rebel groups fought off a small garrison of government troops and swept into the villages, killing 190 people, according to a Human Rights Watch report to be released on Friday. At least 67 of the dead appeared to have been shot or stabbed while unarmed or fleeing, including 48 women and 11 children, the report said. More than 200 civilians are still being held hostage.

“This is the first time that we have documented opposition forces actually systematically targeting civilians,” said Lama Fakih, the group’s deputy director in Beirut, Lebanon, who last month visited five of the villages, which the government had recaptured by Aug. 19. She also reviewed medical records and interviewed 19 witnesses as well as doctors, military officials and opposition members for the 113-page report…

The disclosures in the latest report cast further doubt on the effectiveness of Western efforts to isolate foreign fighters and other extremists within the rebellion and foster a command-and-control structure for the fractured opposition forces. And they seem bound to bolster the government’s strategy of convincing Syrians and world leaders that the alternative to its rule is chaos and extremism.

The groups accused of leading the Latakia operation and committing the bulk of the atrocities include the extremist, foreign-led Islamic State of Iraq and Syria — which is also engaged in armed conflict with rival rebel groups — along with the Nusra Front, Ahrar al-Sham and two other Islamist groups that include foreign fighters.