Syrian security forces shot dead 14 protesters on Friday as tens of thousands of anti-regime demonstrators surged onto the streets after weekly Muslim prayers, and Europe condemned Damascus over its "shocking" crackdown.

The demonstrations came in response to a call by the Facebook group Syrian Revolution 2011, a driving force behind three months of protests against the autocratic rule of President Bashar al-Assad.

"Security forces tried to break up a rally calling for the fall of the regime with tear gas before opening fire," killing five people and wounding 25 others, said an activist in the Damascus neighbourhood of Barzeh reached by telephone.

Activists told AFP in Nicosia dozens of people in Barzeh were arrested in house-to-house searches and a curfew was also imposed there, although it was not clear when it would be lifted.

At least five demonstrators were killed in the town of Kiswah south of Damascus, another activist told AFP.

"Demonstrators left the mosque after Friday prayers and marched for a few minutes until security forces opened fire to disperse them, killing five people and wounding six others," Mohammad Enad Suleiman said.

Three people were killed in Homs and a fourth near the central city when security forces opened fire on protesters, an activist at the scene told AFP.

Demonstrations rocked many other cities, including the eastern oil hub of Deir Ezzor where 30,000 protesters filled the streets, said Rami Abdel Rahman of the London-based Syrian Observatory for Human Rights.

State television blamed the civilian deaths in Barzeh on "armed men," saying they also wounded several security force members including an officer.

It added that a police officer was also shot dead in the Damascus suburb of Kadam, and the official SANA news agency reported that "several members of the security forces were hit by gunfire in Kiswah."

Syria blames the violence on "armed terrorist gangs" and says the protests are being orchestrated from abroad.

Syrian rights groups say that more than 1,300 people have been killed and 10,000 have been arrested in the regime's brutal crackdown on dissent since the protests erupted on March 15.

Friday's protests were held under the slogan "Fall of legitimacy," with a Facebook page message reading: "Bashar is no longer my president and his government no longer represents me."

The crackdown has sent nearly 12,000 Syrians fleeing to safety in neighbouring Turkey, prompting US Secretary of State Hillary Clinton to warn of the risk of regional escalation.

The European Union warned Assad's regime that its legitimacy was undermined by the crackdown.

A declaration adopted at an EU summit in Brussels "condemns in the strongest possible terms the ongoing repression and unacceptable and shocking violence the Syrian regime continues to apply against its own citizens.

"By choosing a path of repression instead of fulfilling its own promises on broad reforms, the regime is calling its legitimacy into question.

"Those responsible for crimes and violence against civilians shall be held accountable."

The EU leaders also called for the UN Security Council to adopt a resolution condemning the crackdown, a move opposed by veto-wielding member Russia.

The EU this week slapped fresh sanctions on Syria, expanding a blacklist targeting 23 top leaders including the embattled Assad and three commanders of Iran's Revolutionary Guard accused of aiding the crackdown.

Damascus reacted angrily to the sanctions, with Foreign Minister Walid Muallem saying they were "equivalent to war" and denying receiving Iranian help.

Meanwhile the number of Syrians sheltering in Turkey has approached 12,000 after some 1,500 refugees poured across the border on Thursday and Friday, officials in Ankara said.

The influx has triggered concern in Washington, particularly as the flow came after Syrian troops stormed border villages including Khirbet al-Joz, where many displaced people had massed, according to activists.

Clinton said the Syrian troop build-up was "worrisome" and could increase the chances of a border clash and "only exacerbate the already unstable refugee situation in Syria."

The EU declaration called for "maximum restraint" following Syrian military activity near the Turkish border.

"What is happening in Syria is quite appalling, thousands of people are being killed, tens of thousands have been interned," British Prime Minister David Cameron said.

The exodus has prompted Turkey to build a giant tent city along the border to expand a Red Crescent camp where more than 200 tents had already been erected.