Peace envoy Lakhdar Brahimi met internal opposition groups Tuesday as he pushed a new initiative to end Syria's conflict, and as Gulf Arab states urged a rapid political transition.
Pope Benedict XVI called in his traditional Christmas message for "an end to the bloodshed" and for "dialogue in the pursuit of a political solution" in Syria.
Brahimi, the UN-Arab League's special envoy to Syria, held talks at his Damascus hotel with a six-strong delegation led by Hassan Abdel Azim, head of the National Coordination Committee for Democratic Change, an opposition group tolerated by the regime.
Azim said afterwards that Brahimi would stay in Syria until Sunday "to try to implement an international consensus to end the crisis."
His deputy Raja Nasser told reporters: "The only solution is a transitional government that holds all powers.
"A political solution is the only solution, and this means the establishment of a new democratic regime instead of the current regime."
A French daily has reported a supposed US-Russian initiative for a transition in Syria, causing rage among opponents who reject any compromise with the regime.
Le Figaro said a solution in the offing would involve keeping Assad in power until 2014 while preventing him from further renewing his mandate.
The Local Coordination Committees, a grassroots network of anti-regime activists, blasted Brahimi and the international community for failing to stop the bloodshed.
At least another 113 people were killed across Syria on Tuesday, including 45 civilians, according to the Syrian Observatory for Human Rights.
In total, more than 44,000 people have been killed since the uprising erupted in March last year, the Observatory estimates.
"Brahimi's arrival in Damascus to discuss a new political initiative to solve the crisis caused by the regime... has not put a stop... to massacres," the LCC said.
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It said the LCC rejects "any initiative that puts Syrians in a position where they are extorted and forced to choose between accepting unfair compromises, or the continuation of the regime's crimes against them."
The opposition Muslim Brotherhood also dismissed any compromise that would leave Assad in power.
"We consider that giving Assad the opportunity to commit an endless string of crimes is tantamount to complicity in these crimes," it said.
Brahimi met Assad on Monday, saying afterwards that they had "exchanged views on the many steps to be taken in the future" regarding the "always worrying" Syrian crisis.
A diplomat at the United Nations said that there was no sign of a breakthrough, with Assad appearing unready to negotiate and the armed opposition ruling out a compromise.
"Assad appears to have stonewalled Brahimi again, the UN Security Council is not even close to showing the envoy the kind of support he needs and the rebels will not now compromise," said the diplomat.
Meanwhile, violence raged southwest of Damascus, mainly in the towns of Moadamiyet al-Sham and Daraya, the Observatory said, adding at least eight people were "summarily executed" by regime forces.
Rebels seized the town of Harem in the northwestern province of Idlib, large swathes of which are now in the hands of anti-regime fighters, it added.
In the northern city of Aleppo, warplanes attacked a rebel-occupied school in the Tareq al-Bab area, said the Observatory which relies on a network of activists and medics for its information.
The Gulf Cooperation Council of six Arab monarchies expressed "deep sadness over the continued shedding of blood by the regime and the destruction of cities and infrastructure, making political transition a demand which must be rapidly implemented."
The Pope in his Christmas message pleaded for a peaceful solution, "easier access for the relief of refugees and the displaced, and dialogue in the pursuit of a political solution to the conflict."
United Nations relief official John Ging warned on Tuesday: "People are losing hope because they just see more violence on the horizon, they just see a deterioration."