The UN-Arab League Joint Special Envoy for Syria Kofi Annan on Saturday expressed his concern over reports of the concentration of troops and heavy weapons around Aleppo, in anticipation of an imminent battle in Syria's largest city.

"I remind the parties to the conflict of their obligations under international humanitarian law and human rights law, and urge them to exercise restraint and avoid any further bloodshed," Annan said in a note to the press.

The escalation of the military build-up in Aleppo and surrounding area, the Joint Special Envoy said, "is further evidence of the need for the international community to come together to persuade the parties that only a political transition, leading to a political settlement will resolve this crisis and bring peace to the Syrian people."

Intense clashes continued in Syria's northern Aleppo province on Saturday, as Syrian army battling to regain control of the rebel-held areas.

The street battles in Aleppo, which is considered the commercial capital of the unrest-hit country, have been heating up for days after the opposition fighters have apparently lost a battle to subdue the capital.

Syrian troops have reportedly surrounded northern Aleppo province from different directions in preparation for an offensive campaign after the armed rebels moved their battle to the northern province, and declared their insurgency to "liberate Aleppo from government troops."