Syrian troops have opened fire on opposition protesters in Deir el-Zour, an eastern city that has been under siege by government forces for several days.
Activists and witnesses say Syrian forces began firing live ammunition at protesters outside at least one mosque in the city following Friday prayers. It was not immediately clear if there were any casualties.
Earlier Friday, Syrian security forces began carrying out raids in anticipation of the mass Friday protests. Rights groups and activists say a woman was killed after tanks and soldiers launched an assault in Khan Sheikhon in the northern province of Idlib.
A man was also shot and killed after fleeing security forces in the town of Saqba, a suburb of the Syrian capital Damascus.
At least 16 people were killed across Syria on Thursday as the government widened its crackdown, despite mounting international condemnation of Syrian President Bashar al-Assad's use of violence against protesters.
Also Thursday, in an interview with CBS News, U.S. Secretary of State Hillary Clinton called on Europe and China to impose additional sanctions on Syria's oil and gas industry.
When asked why the United States has not yet called for Syria's president to step down, Secretary Clinton said it was important that the American voice is not the only one calling for Mr. Assad's removal.
Secretary Clinton has previously said Mr. Assad's government has “lost legitimacy,” but senior American officials have stopped short of explicitly calling on the Syrian president to leave office.
Details of events in Syria are difficult to confirm because the government allows very few foreign news reporters into the country and restricts their movements.
On Thursday, U.S. President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan agreed during a phone call on the need for a transition to democracy and an immediate end to the bloodshed in Syria.
Meanwhile, U.S. Ambassador to Syria Robert Ford met with Syria's Foreign Minister Walid Muallem Thursday in Damascus, where Ford made clear that Syria will face increasing pressure and more economic sanctions if the violence does not stop.
