Syrian forces launched new air strikes and shelled rebel strongholds in several key cities on Saturday, a watchdog said, after the UN named a new envoy to try to end the conflict.

The intensified fighting, particularly in and around the key northern hub of Aleppo, has sent thousands more Syrians fleeing into neighbouring countries as the divided international community appears powerless to act.

The United Nations said Friday that veteran Algerian diplomat Lakhdar Brahimi would take over as international envoy from Kofi Annan, who quit this month after the failure of his peace plan.

And Brahimi admitted he was not confident he would be able to end the 17-month-old conflict, which activists say has killed 23,000 people, while the UN puts the toll at 17,000.

"I might very well fail but we sometimes are lucky and we can get a breakthrough," the 78-year-old told the BBC. "We have got to try. We have got to see that the Syrian people are not abandoned".

His appointment was announced the day after the UN called time on its observer mission in Syria.

UN chief Ban Ki-moon called on the international community to give the new envoy "strong, clear and unified" support, after Annan complained his mission had been hamstrung by the deep rift on the UN Security Council between the West and traditional Damascus allies Beijing and Moscow.

US Secretary of State Hillary Clinton endorsed Brahimi, saying the world community was committed to bringing about change in Syria and "ensuring that those who commit atrocities will be identified and held accountable".

China, which along with Moscow has vetoed Security Council resolutions on Syria and has accused the West of hampering efforts to end the crisis, also vowed to cooperate with Brahimi in the search for a political solution.

On the ground, warplanes bombed the town of Aazaz on Friday, just days after an air strike that flattened homes and killed at least 40 people, the Syrian Observatory for Human Rights said.

Syrian forces also bombarded several areas of Aleppo, the northern commercial hub that has emerged as the main battleground as it is key for control of routes to Turkey -- the rear base for the rebel Free Syrian Army.

Fighting was reported in several districts of the city, the Observatory said, while regime forces also pounded rebel areas of the central city of Homs and the southern city of Herak.

It said a total of 129 people were killed in violence on Friday alone.

-- 'More bodies found dumped ' --

And in a grim sign of the escalating brutality of the conflict, the Observatory said dozens of bodies had been found dumped in several areas of Damascus province.

Opposition factions had reported that another 65 bodies had been found dumped on a rubbish tip in a town near Damascus on Thursday, claiming the victims had been bound, executed and set on fire by pro-government forces.

It is impossible to independently verify such claims as journalists are unable to report freely in Syria.

Government forces appear to be resorting to more attacks from the air against the more poorly armed and disparate rebel groups, while accounts of people being shot dead by snipers are increasing.

In a damning report this week, a UN panel said government forces and their militia allies had committed crimes against humanity including murder and torture, while also accusing the rebels of war crimes, but to a lesser extent.

And the conflict is creating an increasingly precarious humanitarian situation, triggering a major exodus of refugees that the UN said Friday had swelled to least 170,000, many of them fleeing to Turkey.

French Foreign Minister Laurent Fabius called for President Bashar al-Assad's regime to be "smashed fast" as he visited the largest of the refugee camps in Turkey.

"After hearing the refugees and their account of the massacres of the regime, Mr Bashar al-Assad doesn't deserve to be on this earth," Fabius said.

But Russia rejected a proposal to set up no-fly zones to help fleeing civilians after the United States said it was ready to consider the move.

"You have to solve citizen security issues using methods put in practice by international humanitarian law," Foreign Minister Sergei Lavrov told Sky News Arabia.

"But if you try to create no-fly zones and safety zones for military purposes by citing an international crisis -- this is unacceptable," he said.

Fabius also said during his visit to the region that he expected more "spectacular defections" soon.

Assad's minority Alawite-led regime has faced a string of high-level defections, including by prime minister Riad Hijab and senior general Manaf Tlass, and a bomb attack that killed four top security chiefs.

The president has characterised the conflict as a battle against a foreign "terrorist" plot aided by the West and its allies in the region, led by Sunni Muslim powerhouse Saudi Arabia.