Military sources claim more than 20 thousand Syrian troops are surrounding Aleppo.
Heavy fighting is continuing in the country’s second city and rebels still appear to control significant districts.
But jets and heavy artillery continue to pound rebel positions and a full-blown assault is reportedly drawing nearer.
President Bashar al-Assad has described Aleppo as a key battleground that could decide the country’s fate.
Fears of the conflict spreading have been accentuated by the detention of 48 Iranians in Damascus on Saturday by rebel forces.
They claim the captives are members of Iran’s elite Revolutionary Guards and produced an ID card which they say is proof.
But Iran says the detainees are pilgrims and has asked Turkey and Qatar to help secure their release.
A spokesman from the Free Syrian Army is insisting the captives were on a reconnaissance mission in Damascus and warns of targeting all Iranian installations in Syria.
However another opposition source told Al Jazeera the video was fake and designed to cover up the activities of a hardline Sunni Muslim group who are targeting Iranian Shia Muslims visiting Holy sites in Syria.
In Damascus itself the signs of intense fighting are all too obvious. The army claims the rebels have been forced out, the rebels claim they withdrew.