Troops and militiamen loyal to Syrian President Bashar al-Assad on Thursday were accused of new massacres of scores of villagers.
The new report came just hours ahead of a United Nations Security Council session on Assad's brutal 15-month crackdown on a popular uprising against his regime.
If confirmed, the killings of at least 78 people at Mazraat al-Qabeer, near Hama, will pile pressure on world powers to act.
However, analysts say there are few signs they can overcome sharp divisions between Western and Arab states on the one hand, and Assad's defenders in Russia, China and Iran on the other.
Several activists reported women and children were among the dead when the village in central Syria came under artillery bombardment before fighters moved in on the ground and shot and stabbed dozens of people to death.
The Mazraat al-Qabeer slayings echoed descriptions of a massacre of 108 civilians at Houla on May 25, which Western powers blamed on Assad's troops and loyalist "shabbiha" militia.
The Britain-based Syrian Observatory for Human Rights said "shabbiha headed into the area after the shelling and killed dozens of citizens, among them women and children."
Some activists said at least 40 of the dead were women and children.
The Syrian state news agency quoted an official source in Hama describing reports from Mazraat al-Qabeer as "completely false," saying security forces had intervened at the request of residents after a "terrorist group committed ... a monstrous crime,” killing nine women and children.
Syrian authorities have also denied responsibility for the Houla killings, blaming foreign-backed Islamist terrorists.
Shabbiha fighters are drawn mostly from Assad's minority Alawite sect, an offshoot of Shi'ite Islam.
They have been blamed for the killings of civilians from the Sunni Muslim majority, raising fears of an Iraq-style sectarian bloodbath.
Rights activists say at least 13,500 people – most of them civilians – have been killed in Syria's entrenched and bloody Arab Spring uprising.