Beirut: Tens of thousands of Syrian protesters shouted for President Bashar Al Assad's death on Friday 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 said.

Security forces killed at least 14 protesters, according to human rights groups.

The calls for Al 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 Rodham Clinton on Friday 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 Friday 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. The fact that protesters still turned out was a signal that Assad's forces cannot terrify protesters into staying home.

However, within Hama, protesters struggled to turn out in great numbers after soldiers clamped down heavily in the streets, witnesses said. Snipers were stationed on rooftops, and troops surrounded mosques and set up checkpoints to head off any marches.

"There are security checkpoints every 200 meters, they have lists and they're searching people ... the mosques are surrounded by soldiers," a Hama-based activist told The Associated Press by telephone, speaking on condition of anonymity for fear of reprisals.

Dozens of soldiers deployed in Hama's Assi Square, which had been the main converging point for hundreds of thousands of protesters in previous weeks, the activist said.

In the central city of Homs, more than a 1,000 soldiers, security agents and plainclothes policemen were deployed in the city's main square.

At least 14 protesters were killed across the country: Five outside the capital, Damascus" one in Homs and two in Hama" Four in the major northern city Aleppo" one in Deir Al Zour" and one in eastern Idlib province, according to multiple activist groups. Military raids earlier in the day killed at least two people.