Activists say Syrian forces are shelling several neighbourhoods in Aleppo as the battle for control of Syria's largest city rages into its sixth day.
Most fighters believe the bombardments will be followed by a ground campaign to pacify the city, although by Thursday morning reports of massive regime reinforcements had yet to materialise.
A rebel spokesperson told the AFP news agency via Skype, however, that a "large number" of troops have been moved from the northwestern province of Idlib to Aleppo.
Last week, Syrian troops used a similar combination of aerial bombardments and overwhelming ground force to quash a rebel assault on Damascus.
Local activist Mohammed Saeed told the AP news agency that the shelling seems to be random and clashes had spread to key neighbourhoods in the centre of the city.
The Britain-based Syrian Observatory for Human Rights said the fighting and shelling in Aleppo killed 26 people on Wednesday, including many children.
Herve Ladsous, the UN peacekeeping chief, said he had told Syrian officials that without a significant reduction in violence, the remaining 150 UN observers would leave on the expiry of the "final" 30-day extension of the mission's mandate, agreed by the Security Council on July 20.