Anadan - Regime forces blasted a string of rebel-held districts in Syria's most populous city Aleppo with shells and machinegun fire before dawn on Monday, according to activists.
The shelling was focused on the southwest district of Salaheddin, a stronghold of the Free Syrian Army, made up of deserters and armed civilians, said the Syrian Revolution General Commission.
The Local Coordination Committees, made up of activists on the ground, said the eastern neighbourhood of Sakhur was also hit by shells and also by machinegun fire, with regime forces deploying helicopter gunships against the rebels.
The Syrian Observatory for Human Rights, meanwhile, said that clashes between troops and rebels erupted early morning near the airforce intelligence headquarters in Aleppo's Zahraa district.
The violence comes as the army pressed an offensive against rebels in Syria's commercial capital into a third straight day, and followed a day in which at least 67 people were killed across the country, according to the Britain-based Observatory.
The regime assault on rebel-held areas of Aleppo, a city of 2.5 million inhabitants, began after military reinforcements arrived on Saturday.
The United Nations estimates that around 200 000 civilians have fled the fighting in Aleppo and that many more are trapped.
Head of UN humanitarian operations, Valerie Amos, requested that relief organisations be granted "secure access" to the northern city.