The risk of civil war looms large over Syria as army defectors increasingly take aim at regime forces and diplomacy fails to resolve the escalating crisis, experts say.

"We are moving down that track and the longer the international community and the Arab League delay (action), the sooner we will be there," said Salman Shaikh, head of the Brookings Doha Center.

Syrian security forces on Friday shot dead 20 civilians, including four children, in the regions of Hama, Daraa, Homs and Reef Damascus, the Local Coordination Committees said, on the eve of an Arab League deadline for Syria to stop its lethal crackdown on protesters and as Turkey warned of the risk of civil war.

The latest bloodletting came as thousands of protesters took to the streets in defiance of massive security deployments to urge nations to expel Syrian ambassadors, activists said.

More than two dozen websites belonging to the government of Syria are being hosted by servers in the United States, Canada and Germany, according to a report by Canadian researchers.

The report released Thursday said the operations raise legal questions because they may violate Canadian and U.S. sanctions against Syria, which has used police and military forces for the past eight months to put down a popular uprising.

European nations said Thursday they have key Arab support for a U.N. resolution condemning human rights abuses by the Syrian government.

Diplomats from Germany, France and Britain tabled the resolution at the U.N. General Assembly's human rights committee on Thursday for a vote expected next Tuesday, officials said.

The United States on Thursday disagreed with Russia's assessment that attacks by renegade Syrian troops risked plunging Syria into civil war, blaming the regime in Damascus for the violence.

"We think that's an incorrect assessment," U.S. State Department deputy spokesman Mark Toner told reporters after Russian Foreign Minister Sergei Lavrov made the assessment.

Hundreds of Coptic Christians marching in Cairo on Thursday came under attack by assailants throwing stones and bottles and 25 people were lightly injured in subsequent clashes, a security official said.

They were marching to demand justice for the Christian victims of a clash with soldiers in October that left at least 25 people dead, most of them Christians.

Catherine Ashton, the European Union's foreign affairs chief, said Thursday that Syria's President Bashar al-Assad should step aside amid intensifying pressure on his authorities to end violence.

"It's time for President Assad to stand down," Ashton said following talks with Russian Foreign Minister Sergei Lavrov in Moscow.

The U.N. atomic watchdog said Thursday a visit by inspectors to Syria last month made "no progress" in clarifying the use of a suspected covert nuclear reactor allegedly bombed by Israel in 2007.

"Unfortunately, no progress was made in meetings with the Syrian authorities on obtaining the full access which we have requested," International Atomic Energy Agency head Yukiya Amano said.

Rebel troops hit offices of Syria's ruling party on Thursday, a day after a daring raid on an intelligence base that prompted Russia to warn that its longtime ally risks "full-scale civil war."

The rocket-propelled grenade attack in northwestern Idlib province, near Turkey, came as security forces killed eight people, including two children, despite an Arab League ultimatum that Syria halt the bloodshed or risk sanctions.

Iraq's anti-U.S. Shiite cleric Moqtada al-Sadr has expressed support for Syrian President Bashar al-Assad, while noting that he sympathizes with the “revolutionaries” in Syria.

Assad has since March been trying to crush a popular uprising against his government, in which over 3,500 people have been killed, according to U.N. figures.