Aleppo has seen some of the worst of the recent fighting
Violence is continuing in Syria, with opposition activists saying that a warplane may have killed as many as 25 people in a single strike in Aleppo province.
A bomb also exploded near a roundabout in the Jaramana district of Damascus, reports the BBC.
Meanwhile, speaking to the BBC, the new international envoy to Syria, Lakhdar Brahimi, said he viewed his new mission as near-impossible.
He is expected to visit Syria and meet President Bashar al-Assad on Saturday.
In Aleppo, human rights groups said several women and children were among the 25 victims when a building was hit in the town of al-Bab.
Al-Bab, just to the north-east of Aleppo, appears to be largely in rebel hands, and has been heavily pounded by government forces in recent weeks, says the BBC's Jim Muir in Lebanon.
Increasingly, as the conflict deepens, the regime has made fuller use of its air power - attack helicopters and fixed-wing jets - to support its ground forces as they try to root out the lightly-armed rebels from towns, cities and villages all over the country, our correspondent says.
Despite the disparity in firepower and manpower, the government is nowhere near winning what has become a civil war of attrition, but the rebels are also not within sight of victory, our correspondent says.
In the car bombing in the Damascus suburb, there are reports of material damage and casualties, but no figures have been given yet.
The explosion is the second within 10 days targeting the predominantly Druze and Christian area of Jaramana.
Separately, the head of the Red Cross is heading to Syria to meet President Assad to try to improve aid access to civilians.
Brahimi, the new UN-Arab League envoy on Syria, was appointed after his predecessor, Kofi Annan, resigned, saying he no longer saw a way to fulfil his mission after his peace plan failed to achieve a meaningful ceasefire.
"I'm coming into this job with my eyes open, and no illusions," Brahimi told the BBC's Lyse Doucet in an interview in New York. "I know how difficult it is - how nearly impossible. I can't say impossible - [it is] nearly impossible.
Brahimi said he had so far failed to see "any cracks" in the "brick wall" that had defeated Annan - an "intransigent" Syrian government, escalating rebel violence and a paralysed UN Security Council, where China and Russia have vetoed several resolutions aimed at putting pressure on Damascus.
He said he would keep Annan's six-point peace plan - now seen by many as irrelevant - in his "tool box" for possible adaptation, but admitted he "had ideas, but no plan yet", apart from talking to as many people as possible.
Addressing the Syrian government, he said the need for political change in Syria was "fundamental and urgent", but he refused to be drawn on whether President Assad should step down, as the opposition and several Western leaders are demanding.