Syrian opposition fighters retook a strategic base in the northern Aleppo province on Saturday, as shelling killed at least 11 people in nearby Aleppo city.
The Syrian Observatory for Human Rights said that the fighters, including some from two al-Qaeda affiliates, launched a counterattack against regime forces after they captured parts of the 80th Brigade base on Friday.
Observatory director Rami Abdel Rahman said the clashes left at least 53 people killed – 33 rebels and 20 government soldiers.
In Aleppo city, the Observatory said shelling by regime forces killed at least 11 people, including four children.
In the north-western Ashrafiyeh district, which is largely under regime control, five people, two of them children, were killed by mortar fire, the Observatory added.
State television also reported deaths in the area, saying six children had been killed by "terrorists" - its term for opposition fighters.
In clashes that took place in the northeast of the city, six civilians died, the Observatory said, including a woman, a six-month-old baby and a three-year-old.
The fighting came as the main opposition group began a two-day meeting in Istanbul to decide whether they will attend a proposed peace conference the US and Russia are trying to convene in Geneva.
The Syrian National Coalition has demanded that President Bashar al-Assad step down in any transitional Syrian government as a condition for going to Geneva.
Syrian officials say Assad will stay in his post at least until his terms ends in 2014 and that he may run for re-election.
In Cairo, Arab League Secretary-General Nabil Elaraby said that the UN-Arab League's top envoy to Syria, Lakhdar Brahimi, will hold a meeting in early December to decide on a new date and the attendees of the Geneva conference.
"We were saddened and depressed because of the failure of the latest meetings to decide on a date and participants for the conference," Elaraby said, referring to a meeting in Geneva earlier this week that many had hoped would call for holding the talks later this month.
The league had wanted the peace conference to lead to a ceasefire and secure means to deliver humanitarian aid to Syrians, Elaraby said.
More than 120,000 people have been killed in Syria since the conflict erupted in March 2011, according to the Observatory. Millions more have been displaced inside Syria or have fled abroad.