The Syrian National Council, a newly launched anti-regime front, has gained mass support in Syria with many people demanding it be recognised as the country's sole authority, activists said on Monday.

The popular support on Syria's streets for the SNC, forged Sunday in Turkey, comes as US Defence Secretary Leon Panetta predicted it is "a matter of time" before President Bashar al-Assad's regime is ousted by a popular uprising.

"Demonstrations of support" for the SNC were held late on Sunday in main protest hubs including Hama, Homs, Idlib, Daraa, Deir Ezzor and the province of Damascus, according to the Britain-based Syrian Observatory for Human Rights.

Protests were also held in the capital's Al-Qadam neighbourhood despite a heavy security presence, the rights watchdog said.

"The Syrian National Council reunites the forces of the opposition and the peaceful revolution," Paris-based academic Burhan Ghalioun told reporters at Sunday's launch in Istanbul.

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.

Videos posted on Facebook page "Syrian Revolution 2011," one of the motors of the protest movement against Assad, showed demonstrators at Zabadani, 50 kilometres (30 miles) northwest of Damascus, chanting their support for the new group: "Syrian National Council, our sole and legitimate representative."

They also demanded that Assad step down.

In Daraa, the southern flashpoint province where the revolt against Assad's regime began in March, protesters carried banners reading: "We support the Syrian National Council, the sole legitimate representative of the Syrian revolution."

Syrian independent lawmaker Mohammed Habash told AFP he supported "in principle any gathering of the Syrian opposition" and called on the SNC to present "logical and plausible proposals to save the country and to end the bloodletting."

"We are opposed to any foreign intervention because the solution should come from within the country," added Habash, who formed a party called "The Third Way" in a bid to find a solution to the political crisis shaking Syria.

Since mid-March, the country has been rocked by an unprecedented pro-democracy protest movement that the Assad regime has sought to crush using deadly force.

More than 2,700 people have been killed in the unrest, according to the UN High Commissioner for Human Rights in Geneva.

Panetta, speaking in Tel Aviv after meeting his Israeli counterpart, said Assad's days were numbered.

Washington and other foreign capitals, he said, had "made clear Assad should step down."

"While he continues to resist, I think it's very clear that it's a matter of time before that (exit) in fact happens. When it does, we don't know," he said.

The Pentagon chief, in a visit to Israel and the Palestinian territories on Monday, said Assad's regime had lost all credibility through its brutal crackdown on dissent.

"Anytime you kill your own people as indiscriminately as they have over these last number of months, it's pretty clear that they have lost their legitimacy as a government," Panetta said at a news conference with Israeli Defence Minister Ehud Barak.

Panetta, who was CIA director until he took over as defence chief in July, pledged the United States and other countries would keep up pressure on the regime to make way for a government more responsive to the needs of its people.

The violence continued on Monday, with the Observatory reporting security force operations in Douma, about 20 kilometres west of Damascus, in which an unknown number of people were arrested, as well as in Deir Ezzor in the east and at Saraqeb in the northwestern Idlib province.

The group also said the army had Sunday "taken complete control" of the central city of Rastan in Homs province, 160 kilometres north of Damascus, after fighting between army deserters and Syrian forces.

Assad's regime blames the violence raging for more than six months in Syria on "armed groups."