From the BBC:
Rights groups say at least 14 people were shot dead by government troops across the country.
Protests were reported in the capital, Damascus, in eastern and western cities and in towns along the border regions.
US Secretary of State Hillary Clinton has warned time is running out for Syria's government to usher in reforms.
Speaking during a visit to Lithuania, she said President Bashar al-Assad would face more organised resistance to his rule unless the country saw "a genuine transition to democracy".
Human rights groups estimate that about 1,700 people have been killed in three months of protests.
Mr Assad has promised a dialogue on political reforms, but the protesters are calling for him to stand down.
Eleven people have reportedly been killed in Syria, after hundreds of thousands of demonstrators took to the streets across the country in fresh protests against the rule of President Bashar al-Assad.
Witnesses and activists said anti-government protesters were calling on Assad to "leave", braving a security crackdown ordered by the authorities to quell unprecedented protests sweeping the nation since March.
The Local Co-ordination Committees, a network of activists, said five demonstrators were shot dead by security forces on Friday in the central city of Homs, three in the northern province of Idlib, two in Damascus suburbs and one in Latakia.
A huge rally was held in the city of Hama, where people filled the square around the central Clock Tower. Activists said at least 200,000 people were taking part in what they said was the biggest demonstration since the uprising began in March.
"Here we are, the germs of Syria," a local activist said, referring to the president's speech in which he characterised the protesters as "germs" that Syria must inoculate itself against. "But we are big germs in huge numbers."