BEIRUT – Tens of thousands of Syrian protesters shouted for President Bashar Assad’s death 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 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 have grown dramatically in the past five months, 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. U.S. 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.

Security forces broke up protests quickly around the capital of Damascus, in the central city of Homs and elsewhere, firing bullets and tear gas. Some areas saw only limited demonstrations because soldiers were 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 Homs, more than 1,000 soldiers, security agents and plainclothes policemen were deployed in the city’s main square.

Five protesters were killed outside Damascus; one in Homs and two in Hama; four in the major northern city of Aleppo; one in Deir el-Zour; and one in eastern Idlib province, according to multiple activist groups. Military raids earlier in the day killed at least two people.

“Where are the prisoners, Bashar? Free the prisoners, Bashar!” shouted protesters in the Mediterranean coastal city of Latakia, shown in an amateur video posted by activists. Another video showed a crowd outside a mosque in the southern city of Daraa being hit by clouds of tear gas after they chanted for the downfall of the regime.

The Associated Press could not verify the authenticity of the videos. Syria has banned most foreign media and restricted local coverage, making it impossible to get independent confirmation of incidents.

The government has justified its crackdown by saying it was dealing with terrorist gangs and criminals who were fomenting unrest.

The military offensive reflects Assad’s determination to crush the uprising despite mounting international condemnation, including U.S. and European sanctions. A flurry of foreign diplomats have rolled through Damascus, urging Assad to end the campaign of killing.

“We believe that President Assad’s opportunity to lead the transition has passed,” Jay Carney, spokesman for President Obama, told reporters traveling on Air Force One on Thursday.

But the United States and other nations have little power to threaten further isolation or economic punishment of Assad’s pro-Iranian regime — unlike in Egypt, where Obama was able to help usher longtime ally Hosni Mubarak out of power.

On Friday, the Dutch Foreign Ministry said the European Union may decide in the next week or two to broaden its sanctions against the Syrian regime and state-run businesses.

Foreign Minister Uri Rosenthal has been lobbying his colleagues to expand the EU travel ban on Syrian officials — which now covers 35 people, including Assad — and to target Syria’s telecommunications, banking and energy sectors. Syria gets about 28 percent of its revenue from the oil trade.

“We need to cut off the oxygen from the regime through its profitable public enterprises,” Rosenthal said on the ministry’s website.

But the bloody crackdown has continued, along with a nationwide campaign of arrests.

Security forces on Thursday detained Abdul-Karim Rihawi, the Damascus-based head of the Syrian Human Rights League, activists said. A longtime rights activist, Rihawi had been tracking government violations and documenting deaths in Syria.

He was picked up from a cafe in central Damascus along with a journalist who had been interviewing him, according to rights activist Ammar Qurabi.

Italy and France on Friday condemned the arrest and called for Rihawi’s immediate release.