Hundreds of civilians have streamed out of eastern Aleppo by foot as Syrian troops and allied forces waged a relentless campaign to drive rebels from their rapidly crumbling enclave.

Russia says Syria's army has halted its attacks in Aleppo to allow trapped civilians to be evacuated.

Thousands of residents have been fleeing eastern Aleppo after simultaneous advances inside the divided city by Syrian government and Kurdish-led forces.

The UN special envoy for Syria says he is "appalled and shocked" that rebels in western Aleppo are targeting civilians in the city.

Syrian government forces have launched a counter-offensive under the cover of air strikes in an attempt to regain control of areas they had lost to insurgents the day before in Aleppo, activists and state media said.

Russia has warned the US against carrying out any attacks on Syrian government forces, claiming there would be repercussions across the Middle East.