Half of the victims in yesterday's attack were civilians, including women, while the other half were village fighters defending their homes in Maan in the province of Hama, said the British-based Syrian Observatory for Human Rights.
Syrian state media described the attack as a "massacre" perpetrated by terrorists, a term the government uses to describe rebels fighting to topple President Bashar Assad.
Extremist Sunni Islamic fighters have come to dominate the armed uprising against Assad, who is a member of the Alawite sect, an offshoot of Shiite Islam.
The reports of the Maan attack came as Syrian government and opposition delegates started a fresh round of UN-brokered peace talks in Geneva. The first face-to-face meetings adjourned 10 days ago having achieved little beyond getting the warring sides into the same room.
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Prospects for common ground appear unlikely as the two sides continue to disagree on the core issue of Assad's future. Fighting has escalated since the first round, with violence disrupting food distribution meant to ease the plight of civilians in the central city of Homs and near Damascus.
Abdurrahman said the Islamic fighters overran Maan after Alawite villagers lobbed mortar shells on the rebels using the nearby roads.
There have been heavy clashes for weeks between hard-line rebels and Assad loyalists in the nearby community of Morek, Abdurrahman said.