Thousands of Syrian army troops have joined the fierce fighting in Aleppo after being redeployed from positions close to the Turkish border.
The country’s second city has been the centre of bloody battles all week, with government jets deployed for first time since the uprising began.
Rebels say they have launched attacks on military convoys heading towards Aleppo.
After forces loyal to Assad mounted a massive counter-offensive in Damascus footage has emerged that purports to show the victims of an alleged massacre carried out by the Syrian army in the Qaboun district of the capital.
For the moment most of the regime’s attention appears to be focussed on Aleppo because of its commercial and strategic importance.
The UN has withdrawn half of its 300 strong monitoring mission as the violence and chaos continues without let up.
Secretary General of Peacekeeping Operations, Herve Ladsous said: “About half of the military observers have been for the time being sent back to their countries. So the mission operates on a reduced basis, reduced in numbers, reduced in team sites in the provinces and does what it can”.
Earlier Turkey closed its border with Syria to commercial traffic, but the UN refugee agency says the frontier would remain open for those fleeing the conflict.