Clashes in Syria's largest city Aleppo continued throughout the night, as President Bashar al-Assad's forces remain locked in a fierce battle with armed rebels.

At least two dozen people were reported to have been killed as the regime's tanks and helicopter gunships attacked on Saturday. Latest reports suggest that the regime's forces are gaining the upper hand.

However, Syrian troops have failed to capture the rebel stronghold in Aleppo as they were outnumbered by the forces of the Free Syrian Army (FSA), which some reports say are over 1,000-strong.

As the fighting continued, opposition activists urged western powers to intervene, despite opposition from UN Security Council members Russia and China.

"Our friends and allies will bear responsibility for what is happening in Aleppo if they do not move soon. Any action has to be from outside the Security Council through an Arab League initiative and through a resolution passed by the General Assembly," said the head of the Syrian National Council, Abdelbasset Sida, according to Reuters.

Sida also asked western nations to provide weapons to take on the tanks and jet fighters of the Syrian regime. He also insisted that Assad be tried for his massacres in Syria.

World leaders and the international community have voiced their concern over the possibility of a massacre in Aleppo.

"I am concerned about reports of the concentration of troops and heavy weapons around Aleppo, in anticipation of an imminent battle. The escalation of the military build-up in Aleppo and the surrounding area 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," UN and Arab League special envoy Kofi Annan said in a statement.

Aleppo is of vital importance to both factions in the civil war as it is the commercial capital of Syria, and victory for either side will give it a strategic advantage.