At least 21 people are dead after Syrian forces fired live rounds into crowds of protesters as thousands took to the streets for pro-democracy demonstrations, according to Reuters.
The attacks took place in the suburbs of Damascus, Hama and Deraa, according to Al-Jazeera.
Witnesses say 11 and 16-year-old boys are among the dead, Al-Jazeera reports.
One of the attacks took place after Syria's secret police drove cars into the demonstrators trying to break up a protest. After one of the cars crashed, police jumped out and opened fire, according to Al-Jazeera.
"The four secret police officers opened fire on the protesters with machine guns," one witness told the Arab-based network.
Syria has launched a bloody crackdown over the past two months on an unprecedented uprising against Syrian President Bashar Assad, unleashing the army and security forces to crush dissent. Human rights groups say more than 850 people have been killed in the crackdown.
The latest round of violence comes as Syria accused the United States of meddling after President Obama said that the Syrian president should lead his country to democracy or "get out of the way."
Syria's official news agency said Obama's speech amounted to "incitement."
The comments by the U.S. president on Thursday were his most direct warning to Assad, whose regime is trying to crush a popular revolt.
"Obama's speech confirms the reality of American intervention in the internal affairs of the region's countries, including Syria," the statement said.
Syria has launched a bloody crackdown over the past two months on an unprecedented uprising, unleashing the army and security forces to crush dissent. More than 850 people have been killed in the crackdown, human rights groups say.
In Banias, a witness said security forces dispersed protesters with gunfire and sticks. Several people were wounded from beatings, including a woman who was taking video of the march. Another Banias resident said authorities imposed a curfew after breaking up the protest.
"They are arresting anyone they see on the street," he said.
Like most witnesses contacted by The Associated Press, the residents asked that their names not be used in fear of reprisals from the government.
Last week, mass arrests and heavy security kept crowds below previous levels seen during the uprising, suggesting Assad's sweeping campaign of intimidation was working. But the marches Friday suggested that opposition forces could be trying to regroup.
Rami Abdul-Rahman, directory of the Syrian Observatory for Human Rights, said Friday's protests were more widespread and larger than the previous week.
"There were large numbers from the south to the north to the suburbs, and there were protests in besieged cities and towns," he said. "Despite the heavy security and military presence in almost all these places, people staged protests calling for freedom. This is very significant."
Also Friday, leading Sunni Muslim cleric Sheik Karim Rajeh, the imam of Damascus's Al-Hassan mosque, said he will no longer lead Friday sermons because security forces have been preventing people from going to prayers. The weekly demonstrations mostly kick off after prayers.
Syria has banned foreign journalists and prevented local reporters from covering trouble spots, making it nearly impossible to independently verify witness accounts.
The Associated Press contributed to this report.