Syrian troops and rebels clashed on Friday in the city of Aleppo, where several people died when a shell crashed into a bakery as hundreds of residents queued for bread.
AFP correspondents said around a dozen people, including three children, were killed and 20 wounded at the bakery in the eastern Tariq al-Bab district of the increasingly desperate city.
And troops repelled a rebel attack on Aleppo's international airport, state news agency SANA reported.
"Mercenary terrorists" had tried to attack it but the "army hit back and killed most of them."
In the latest clashes, Aleppo's historic Citadel, part of a UNESCO-listed world heritage site, was heavily damaged by bombing, the opposition said.
The violence raged on as world powers prepared to name veteran Algerian diplomat Lakhdar Brahimi as their new envoy to seek an end to a 17-month uprising that has cost more than 21,000 lives.
Washington, meanwhile, upped the pressure on Damascus by imposing fresh sanctions on the regime and on the Lebanese militant group Hezbollah, a close ally of Damascus and Tehran.
A rebel commander, Hossam Abu Mohammed, said his men were still fighting in parts of Aleppo's southwestern district of Salaheddin after most fled yesterday in the face of heavy bombing and advancing troops.
"We will not let Salaheddin go," the Free Syrian Army's Abu Mohammed told AFP by telephone on the third day of a government offensive to take the city.
And one of the fighters told AFP the rebels were keeping at bay troops who control a key roundabout from advancing further into Salaheddin.
"They have a few soldiers at the roundabout and some snipers. What we are doing now is preventing the troops from advancing," the fighter said on condition of anonymity.
The army again bombed parts of Salaheddin, as well as the Sakhur and Hanano districts in the northeast, the Syrian Observatory for Human Rights said.
At least 82 people were killed nationwide today, including 35 civilians, the watchdog said. One of those killed was a 19-year-old protester shot dead by regime forces in Aleppo.
Before dawn, a MiG 21 fighter jet dropped four bombs on rebel positions in Hanano, an AFP correspondent said. One struck the courtyard of an FSA compound and another struck a nearby house, wounding a number of people.
Angry residents shouted hostile slogans against France and the United States, saying: "No one is helping us."
The opposition Syrian National Council said Aleppo's 13th-century Citadel, part of a complex of sites in the city's historic heart that the UN Educational, Scientific and Cultural Organisation says is of "outstanding universal value" had been damaged in army shelling.