Activists said there had been gunfire and explosions in the district of Bab Amr and nearby villages, killing at least nine people and wounding dozens.
Several towns around the southern city of Deraa were also raided and at least eight civilians killed, activists said.
Thousands have reportedly been arrested and hundreds killed in the crackdown.
The Syrian government has insisted it is pursuing "armed terrorist gangs", and blamed them for the deaths of two soldiers on Wednesday.
Meanwhile, international pressure has caused Syria to drop its plans to run for a seat on the UN Human Rights Council. Kuwait would take its place, India's deputy permanent representative Manjeev Singh Puri said.
UN Secretary General Ban Ki-moon called on President Bashar al-Assad to "heed calls for reform and freedom and to desist from excessive force and mass arrest of peaceful demonstrators".
Mr Ban said he was disappointed that a UN humanitarian team had not yet been allowed into Deraa, where the unrest began in mid-March.
The UK Foreign Office described the level of repression as "shocking" and urged the Syrian government to change its behaviour. BBC NEWS
