Syrian troops killed at least 15 people and recaptured villages in the central province of Hama, the Syrian Observatory for Human Rights reported on Saturday.
Official media reported that loyalist forces seized control of three villages in Hama province that had been in rebel hands, but did not mention casualties.
The Observatory said the 15 died when troops backed by pro-regime militiamen stormed the Sunni village of Sheikh Hadid late on Friday.
The watchdog, which relies on a network of doctors and medics on the ground for its information, described the killings as a "massacre".
"Fifteen people were killed -- two women, a child and 12 men -- by regime forces backed by the Popular Committees and National Defence Forces Alawite militias using guns and knives," it said.
Ten other people were wounded, it added.
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Syrian President Bashar al-Assad comes from the Alawite minority community, and is battling a rebellion dominated by Sunni Muslims.
The Observatory said there had been clashes between rebels and regime forces in the village, but it was not clear whether the men killed were civilians or insurgents.
State news agency SANA reported that regular troops entered Sheikh Hadid to "restore security and stability" and clear it of diehard jihadist fighters of Al-Nusra Front.
SANA did not mention any casualties in Sheikh Hadid, but said the army also recaptured two other villages in Hama province, Tell Malh and Jelma.
The Observatory also reported that troops had seized Tell Malh and Jelma which had been in rebel hands following fierce clashes.
The Britain-based group also reported air strikes by regime aircraft on targets around the country, namely in the provinces of Damascus, Aleppo and Hama.