Syrian forces on Thursday began the third consecutive day of a crackdown on activists and defectors in al-Rastan city, located in Homs province, dpa reported.
"At least 20 people were killed, among them 10 army defectors," an activist from al-Rastan based in Lebanon told the German Press Agency dpa.
"The intensity of the shelling by tanks and helicopters on al- Rastan increased at dawn, as clashes between the attacking regime forces and the army defectors continued throughout the night," he said.
He added that scores of people were injured in the morning shelling but did not give a specific number.
Al-Rastan has since Tuesday seen clashes between deserters from the forces and the Syrian army.
Homs and its surrounding areas have witnessed street protests against President Bashar al-Assad since the beginning of the six-month uprising.
The crackdown has left 2,700 dead nationwide, according to UN estimates.