Three people have been reportedly killed by security forces after thousands of Syrians shouting "We want freedom!" took to the streets around the country.
Security agents tried to beat them back with gunfire, tear gas and batons, according to an activist.
Two weeks of unprecedented protests in Syria have proved the most serious challenge yet to a four-decade ruling dynasty by the Assad family - one of the most rigid and authoritarian regimes in the Middle East.
Activists dubbed Friday a "Day of Martyrs" and called for mass demonstrations to honour more than 70 people killed since the protests began in mid-March.
The death toll was unclear. One Syrian activist living in exile said he had been told by eyewitnesses that at least three people were killed.
Protests erupted around the country, including neighbourhoods outside the capital, Damascus, and in the southern city of Daraa, which has become the epicentre for the protests.
Several eyewitnesses said by telephone that up to 5,000 people were marching in Daraa, shouting "We want freedom!" and "The blood of martyrs is not cheap!"
The account could not be independently confirmed because the media are under heavy restrictions in Syria. Two Associated Press journalists were ordered to leave the country with less than one hour's notice.
For the first time on Friday, the government acknowledged there were pro-reform gatherings in cities including Daraa and Latakia, but said there was no friction between security forces and protesters.
President Bashar Assad dashed expectations he would announce sweeping changes this week and instead announced that he would form committees to look into civilian deaths and the possibility of replacing decades-old emergency laws. He also blamed the popular fury that has gripped Syria on a foreign conspiracy - enraging protesters who had expected him to announce reforms.