The killing of workers near al-Qusair in western Syria comes a week after the death of over 100 people, including women and children, in Houla.
Twelve workers were killed near Syria's western town of al-Qusair when gunmen loyal to President Bashar al-Assad ordered them off a bus and shot them, activists said on Friday, but Syrian media blamed "terrorists" for the killings.
Thursday's killings follow last week's massacre in the Houla region northwest of Homs where the United Nations said 108 people - mainly women and children - were killed in attacks which it said were probably committed by pro-government forces.
The bloodshed in Houla triggered international outrage. Several Western countries expelled Syrian diplomats and demanded tough action against Damascus at the United Nations.
Damascus said a preliminary investigation showed the Houla killings were carried out by gunmen seeking to force foreign military intervention in Syria.
Video released by activists showed bloodied corpses of at least 10 men laid out on the ground near the town of al-Qusair, which like Houla lies about 20km from the opposition stronghold of Homs city. Qusair is southwest of Homs, near the Lebanese border.
Hamza Al-Buweida, a local opposition activist, said he spoke to a survivor who said the dead men had been returning from work at a fertilizer company in al-Buweida al-Sharqiya.
"They stopped, as usual, at a Syrian army checkpoint. But about 300 meters after the checkpoint a yellow car with four armed shabbiha (pro-Assad militia) stopped their car," he told Reuters over Skype.
"They took money off the men and then killed them one by one with gunshots to the head. More than 300 bullets were found in the bodies," he said.
It was impossible to verify Buweida's account of the killing. Syria has restricted journalists' access since the start of the uprising against Assad 15 months ago.