Syrian security forces have surrounded mosques in rebellious cities to prevent worshippers from pouring into the streets for anti-government rallies after Friday prayers as protesters vowed to choose death over humiliation at the hands of the regime.
The troops fanned out in cities including Daraa in the south and Deir el-Zour in the east, according to the London-based Syrian Observatory for Human Rights.
Syria has banned foreign journalists and restricted local coverage, making it difficult to independently confirm events on the ground.
The five-month-old uprising shows no sign of slowing down, despite a brutal government crackdown that the UN estimates has killed 2,200 people since March. Protesters pour into the streets every week, despite the near certainty of meeting a barrage of shells and sniper fire.
But the regime is in no imminent danger of collapse, setting the stage for a deadly stalemate.
On Friday, which has emerged as the main day for protests in the Arab world, rallies were being held under the banner "Death Rather Than Humiliation".
The United States and Britain called for a tougher stance over Syria's crackdown on protesters on Thursday, demanding new international sanctions on President Bashar Assad and his regime.
In a round of talks on the sidelines of a Paris summit on Libya, the US, Britain and France discussed plans to escalate international action aimed at halting the violence.
"President Assad's brutality against unarmed citizens has outraged the region, the world and most importantly the Syrian people themselves," US Secretary of State Hillary Clinton said in Paris.
In what appeared to be a high-profile defection from the regime, a Syrian attorney general appeared on video late on Wednesday declaring his resignation in protest at the crackdown.
Adnan Bakkour, attorney general for the central Hama province, said security forces killed hundreds of people in the restive city of Hama and arrested thousands of "peaceful protesters".