Activists said large crowds marched in the city of Homs, where the army and militia loyal to Assad raided several districts this week, and in the eastern city of Deir al-Zor, which was stormed by tanks last month.
Protests also broke out in suburbs of the capital Damascus, the Kurdish northeast, the northwestern province of Idlib near Turkey and in southern Syria near Jordan.
Assad has responded to the unrest, inspired by Arab popular uprisings that have toppled three autocratic leaders in North Africa this year, with military assaults in which the United Nations says 2,200 people have died.
“The Syrian people demand international protection for civilians,” read a banner in Idlib.
In Hajar al-Aswad, on the southern edge of Damascus, protesters carried a green, white and red-striped old Syrian flag, dating back half a century to the era before Assad’s Ba’ath Party seized control of Syria.
“After all these killings and assaults, where is international protection?” read a banner carried by protesters who chanted: “The people want the execution of the president.”
Yesterday’s protests echoed the first direct call on Thursday by the Syrian opposition for foreign intervention.
The Syrian Revolution General Commission, an umbrella bloc of activists, appealed to world powers to send human rights monitors to help deter military attacks on civilians.