"Dozens of tanks at dawn encircled the towns of Rastan and Talbisa, as well as the village of Deir Maaleh," the activist told the AFP wire service in Nicosia by telephone.
The three places are situated between Homs and Hama in the centre of the country.
Tanks also blocked the highway linking Homs, which is Syria’s third-largest city
and a flashpoint of pro-democracy protests, to Hama, he said.
Security forces killed at least 12 protesters on Friday, activists said.
More than 1,000 people have been killed and 10,000 others arrested since the revolt began, according to rights groups, while the authorities say 143 members of security forces have been killed.
Foreign journalists are barred from travelling insides the country, making it difficult to report on the unrest and verify witness accounts.