Syrian forces pounded rebel hubs in the city of Aleppo and battled opposition fighters around Damascus on Friday, activists said, as the UN reported a surge in refugees and named a new envoy to try to end the conflict.
The United Nations announced that veteran Algerian diplomat Lakhdar Brahimi will take over as international envoy from Kofi Annan, who quit earlier this month.
In his first tentative comments, Brahimi admitted he was not over-confident he would be able to end the 17-month-old conflict.
"I might very well fail but we sometimes are lucky and we can get a breakthrough," he told the BBC in an interview. But "these missions have to be undertaken. We have got to try. We have got to see that the Syrian people are not abandoned."
On the ground, violence was also reported in other towns and villages across the country, with the bloodletting showing no signs of any let-up a day after the United Nations formally called time on its observer mission.
"The violence and the suffering in Syria must come to an end," UN chief Ban Ki-moon said in a statement announcing the appointment of Brahimi.
Ban called on the international community to give "strong, clear and unified" support to the new envoy, after Annan complained that his mission had been mission had been hamstrung by the deep rift on the UN Security Council between the West and traditional Damascus allies Beijing and Moscow.
But in sign that the divisions remain as large as ever, Washington called for clarifications on Brahimi's mandate and Moscow called off a meeting on the conflict that had been planned for Friday after Western and Arab governments said they would not attend.
On the ground, at least 72 people were killed as the regime continued its onslaught on Friday, according to the Syrian Observatory for Human rights, a watchdog which has a network of activists on the ground.
The army clashed with rebels near the main military airport in Damascus and shelled southern parts of the capital as well as areas of the commercial city of Aleppo and the eastern province of Deir Ezzor, the Observatory said.
Deadly violence was also reported in the provinces of Homs and Daraa, the cradle of the uprising that began with peaceful protests in March 2011 but has escalated into an increasingly vicious battle between armed rebels and government forces.
Opposition factions reported that 65 bodies had been found dumped on a rubbish tip in a town near Damascus, claiming the victims had been bound, executed and set on fire by pro-government forces.
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With the international community still deeply divided over how to end the conflict, the UN said the number of Syrians seeking refuge in neighbouring countries had now soared to at least 170,000.
"There has been a further sharp rise in the number of Syrians fleeing to Turkey," the UN refugee agency said.
French Foreign Minister Laurent Fabius called for President Bashar al-Assad's regime to be "smashed fast" as he visited Turkey's largest refugee camp near the border.
"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.
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.
More than 23,000 people have died since the revolt against Assad's iron-fisted rule broke out, according to activists, while the UN puts the toll at around 17,000.
Assad has described the conflict as a battle for the very survival of his minority Alawite-led regime against a foreign "terrorist" plot aided by the West and its allies in the region.
But he 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 security chiefs.
"It is clear that both sides have chosen the path of war... and the space for political dialogue and cessation of hostilities and mediation is very reduced at this point," UN assistant secretary general for peacekeeping Edmond Mulet said.
And 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.
As the two sides become more entrenched in Syria, there are fears the conflict could spread further afield, after mass kidnappings in Lebanon in retaliation for events across the border.
The United States warned that its nationals face increased threats in Lebanon, including the possibility of targeted kidnappings or terrorist attacks, after several Arab states in the Gulf ordered their nationals to leave.