Tens of thousands of Syrian protesters shouted for President Bashar Assad's death in a dramatic escalation of their rage and frustration, defying bullets and rooftop snipers after more than a week of intensified military assaults on rebellious cities, activists and witnesses have said.
Security forces killed at least 14 protesters, according to human rights groups.
The calls for Mr Assad's execution were a stark sign of how much the protest movement has changed since it erupted in March seeking minor reforms but making no calls for regime change.
The protests grew dramatically over the five months that followed, driven in part by anger over the government's bloody crackdown in which rights groups say at least 1,700 civilians have been killed.
But with the regime shrugging off even the most blistering condemnation, the uprising has become a test of endurance as both sides draw on a deep well of energy and conviction.
US Secretary of State Hillary Clinton urged countries to stop buying Syrian oil and gas or selling the regime weapons, saying those who still do so must "get on the right side of history".
In cities around Syria, protesters chanted, "The people want to execute the president!" during the now-familiar cycle of weekly demonstrations followed by a swift crackdown by the military, security forces and pro-government gunmen who operate on the regime's behalf.
Security forces broke up protests quickly around the capital Damascus, in the central city of Homs and elsewhere, firing bullets and tear gas. Some areas saw only limited demonstrations because soldiers deployed heavily in restive areas.
In a significant show of defiance, some of the largest protests were on the outskirts of the central city of Hama and in the eastern city of Deir el-Zour, where government forces seized control in major military offensives during the past week.