Fierce clashes have flared for a fourth day in Syria's commercial capital of Aleppo, showing the strength of the rebel assault on regime targets.
President Barack Obama warned Syria against using its chemical weapons after Damascus acknowledged for the first time on Monday that they possessed them and threatened their use against any "foreign aggression."
The state news agency said regime forces fought with rebels in the Aleppo neighbourhoods of Salaheddine and Sukkari and claimed they had inflicted heavy losses. The Britain-based Syria Observatory, meanwhile, reported heavy fighting after midnight in several other neighbourhoods as well as shelling by regime forces.
Some areas also saw protests calling for the fall of the government early in the morning, the Observatory reported.
On Sunday a newly formed alliance of rebel groups called the Brigade for Unification announced an operation to liberate Aleppo, the country's largest city with about three million people. Reports from opposition activists indicate the fighting has been restricted to certain outer neighbourhoods and has not reached the city centre.
Damascus, which saw an even fiercer rebel assault last week, appears to be largely in government hands once more as government troops scoured neighbourhoods for the remnants of rebel fighters, the state news agency reported.
Syria warned the international community that it had chemical weapons and would use them in the case of any international aggression. The regime said it would not use them against its own people.
There had been fears that the embattled regime would use chemical weapons as a final desperate measure against the 17-month old rebellion. But the promise not to use them against Syrians was not entirely reassuring because officials have long characterised the rebels as foreign terrorists.
Syria has become increasingly isolated on the international stage, with just regional ally Iran in its corner, as well as Russia and China protecting it from condemnation by the UN Security Council.
Most of its neighbours, however, have become increasingly hostile, including regional powerhouse Turkey. At a political rally Turkish Prime Minister Recep Erdogan predicted the imminent end of the regime. Syrian rebel leaders operate on Turkish soil and arms for the opposition are believed to be entering the country from Turke