Syrian opposition movements announced the formation of a "historic" united front against President Bashar al-Assad's regime at a meeting in Turkey on Sunday.
At home, meanwhile, a son of Syria's grand mufti was killed when his car came under attack from gunmen, Syria's state news agency SANA said.
And rights activists said that Syrian troops have taken control of the central city of Rastan after sending in 250 tanks to quell clashes between the army and deserters.
"The Syrian National Council reunites the forces of the opposition and the peaceful revolution," Paris-based academic Burhan Ghalioun told reporters in Istanbul, announcing the new umbrella movement which he called "historic."
Uniting groups across the political spectrum, "it represents the Syrian revolution both inside and outside the country," he said.
"It works to mobilise all categories of people in Syria and give the necessary support for the revolution to progress and realise the aspirations of our people for the overthrow of the regime, its symbols and its head," he said.
Ghalioun said the SNC was "open to all Syrians."
The SNC called on "international organisations to assume their responsibility toward the Syrian people and to work to protect them from the war declared against them, to halt ... the dangerous human rights violations."
But "the council rejects any outside interference that undermines the sovereignty of the Syrian people," he added.
Ghalioun is to chair the SNC, whose board will include Bassma Kodmani as spokeswoman, Mohammed Riyad al-Shaqfa of the Muslim Brotherhood and representatives of the so-called Damascus Declaration for reform.
The new grouping is to hold a general assembly of 190 members at the beginning of next month, "probably in Turkey," Kodmani said.
The SNC, which is to elect a president, will have a 29-strong general secretariat representing seven Syrian opposition factions.
SNC member Hassan Hashimi said they would comprise six members of the Local Coordination Committees, five Brotherhood and tribal representatives, four of the Damascus Declaration and four for a liberal grouping led by Ghalioun.
The remaining members of the secretariat would be five independents, four Kurds and a Christian, he said.
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The separate opposition factions will also be represented in a seven-strong executive committee, Hashimi said.
Representatives of Syria's six-month-old protests and opposition met at the weekend against the backdrop of an uprising which the UN says has cost at least 2,700 lives since it erupted in mid-March.
On the ground, the Syrian Observatory for Human Rights said the army had "taken complete control of Rastan, and 50 tanks left on Sunday" the town in Homs province, 160 kilometres (100 miles) north of Damascus.
"Many houses have been destroyed there and the humanitarian situation is very bad," the Britain-based rights watchdog said.
"We have information that dozens of civilians were killed and buried in the gardens of houses as the army shelled the town," it added.
Officers who had deserted announced their "retreat from Rastan" in a statement on Friday night.
Three people were reported killed in clashes in Rastan on Saturday between the army and deserters as the Assad regime pursued its deadly crackdown on dissent.
The Syrian Observatory reported the arrest in Homs of Mansur Atassi, 63, a leader of a coalition of opposition groups, saying he was detained in his office by security agents.
It also said the bodies of three civilians detained since Thursday were returned to their families in Khan Sheikhun near the border with Turkey in Idlib province.
State news agency SANA said Saria Hussein, a son of Grand Mufti Ahmad Badreddin Hassoun, Syria's chief Sunni religious figure, and history professor Mohammed al-Omar were killed "by gunfire from a group of armed terrorists."
The two were attacked while travelling in the professor's car on the Aleppo-Idlib road in northwest Syria, it said, after having earlier reported that the grand mufti's son was injured.
The Observatory also reported the death of Hassoun, saying the attack was carried out by "unknown assailants."
SANA earlier reported that a train driver and his helper were injured in an accident caused by an "armed terrorist group" at Ubin in Idlib province.
Assad's regime blames the violence raging for more than six months in Syria on "armed groups."