Armed groups opened fire on citizens and security forces in the Damascus suburb of Douma and in the city of Homs, the Syrian state news agency reported on Friday, quoting an official source.
The SANA agency said several people were killed and wounded.
"An official source said an armed group took to the rooftops of some buildings in Douma after midday and opened fire on hundreds of citizens gathering in the city and on security forces," it said.
"In the city of Homs, an armed group opened fire on a gathering of citizens in the Bayyada district, which resulted in the death of a girl," SANA added.
Earlier in the day, the Al Arabiya television network reported that ten protesters where killed across Syria during a government crackdown on anti-government protests.
Arab media reported that protesters were killed in the cities of Daraa, Latakia, Homs, Kamishli, and in Damascus.
The extraordinary wave of demonstrations has 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.
The government blamed Friday's violence on armed gangs in a rare acknowledgment of the violence.
Activists dubbed Friday a Day of Martyrs and called for mass demonstrations to honor more than 70 people killed since the protests began in mid-March. An activist in Douma, just outside the capital, said he and hundreds of others came under attack by security forces as they left the town's Grand Mosque, chanting slogans for freedom.
He said the troops hit people with clubs and threw stones before firing tear gas and finally live ammunition.
"I saw three people dead and six wounded," the activist said. Douma's streets are now totally empty except for security forces of whom some are in plainclothes.
Other protests took place in the southern city of Daraa, which has become the epicenter for the protests.
Several eyewitnesses told The Associated Press 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. On Friday, two Associated Press journalists were ordered to leave the country with less than one hour's notice.
The witnesses who spoke to the AP asked that their names not be published for fear of reprisals.
For the first time 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.
The United States responded to the violence in Syria on Friday, with White House spokesman Jay Carney saying that the U.S. administration was "working with our allies in the region and speaking directly or, rather, publicly to the Syrian government urging them to cease the violence and to engage in national dialogue."
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 Assad to announce reforms.
Scores of plainclothes security agents deployed Friday in Damascus near the historic Umayyad mosque, where only last week, pro- and anti-government crowds clashed, hitting each other with leather belts.
As people began leaving the mosque Friday, a crowd of at least 300 people carrying Syrian flags and pictures of Assad broke out into clapping and chants of "Allah, Syria, Bashar!" Security forces made no attempt to stop them.
A Syrian in Lebanon who was in touch with eyewitnesses in the northeastern city of Qamishli said thousands were protesting there in solidarity with Daraa, chanting peaceful, peaceful.
In the central city of Homs, one witness said pro- and anti-Assad crowds were fighting with sticks.
Dozens of people were wounded and many others arrested, said the witness.
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