Syrian Foreign Minister Walid al-Muallem said on an unannounced visit to key ally Iran yesterday that Rebels fighting government forces in Syria's commercial capital Aleppo "will definitely be defeated".

His assertion came as Syrian troops, backed by air power and tanks, pushed on in the second day of an assault on the northern city of Aleppo, sparking international fears of a humanitarian catastrophe.

Salehi warned that, if the Syria conflict worsened and the regime of President Bashar al-Assad fell, the consequences "would engulf the region and eventually the whole world."