The crackdown comes one day before the Islamic holy fasting month of Ramazan, which starts on Monday. Protesters have vowed to hold protests every night during Ramazan and continue until dawn. Activists wrote on the Syria Revolution page online that "if this campaign fails to achieve its goal, it will mark the beginning of the end for the regime."
At least 100 people were killed when the Syrian army stormed the flashpoint central city of Hama. "Hama is used to massacres by the Assad family, but we tell this tyrant the more you kill us, the more we are determined to oust you," an activist, who requested anonymity, told the German Press Agency by phone.
In 1982, a government crackdown left more than 20,000 dead in the city, when the town's Sunni population attempted to revolt against then president Hafez al-Assad's minority Alawite sect.
On Sunday, tanks stormed the city at dawn, shelling different neighbourhoods. Electricity and water supplies to the main areas were cut before the attack began.
Troops surrounded one of the major hospitals to prevent the wounded from reaching it. Over 100 people were injured in the attacks.
Activists also said that four buses filled with security forces personnel arrived at the Southern entrance of Hama, located around 200 kilometres north of Damascus.
Local human rights advocates say that around 1,600 civilians have been killed since protests calling for the ouster of al-Assad began in mid-March. Over 350 security personnel have also been killed.
In the southern Harak town, in Daraa province, several people, among them a 3-year-old girl, were killed after security forces stormed the town.
Tanks surrounded Harak and black smoke was covering the city and no one can reach the town as all roads are blocked, an activist in the provincial capital Daraa said.
In the eastern city of Deir el-Zour, at least 19 people were killed when tanks stormed al-Joura district early Sunday. Dozens were injured, activists said. At least two were also killed in the northern Idlib city.
Tanks entered the Damascus suburb of Moadamiyya, while government forces used tear gas to break a demonstration of around 1,000 protesters in the Daraya suburb who were chanting for toppling the regime and in support of cities under military attacks, the Local Co-ordination Committees of Syria said in its online group.