Clashes in Aleppo have unleashed a wave of unprecedented violence across Syria's second city that has seen some of the worst brutality of the country's six year civil war. Inhabitants, some 250,000 of them trapped in besieged rebel-held areas, have taken to burning barricades of tyres in the streets to blind warplanes flying overhead to targets below.

The London-based Syria observatory has called the fighting "the most violent attack ever carried out by the factions" as rebel forces attempt to break through a siege on the east of the city by regime forces.

Rebels made a series of gains in south and western Aleppo despite heavy aerial bombardment. The surge in violence in the city appears to be linked to a move by al-Qaeda's affiliate in Syria Jahbat al-Nusra to sever its ties to the international terror group.

The rebranding of the extremist paramilitary group has bolstered the ranks of the rebel forces, which had suffered a series of defeats in Aleppo in recent weeks, united against Syrian President Bashar al-Assad.

The Russian Defence Ministry has admitted one of its helicopters was shot down on Monday (1 August) near Aleppo, Syria, with five people on board, according to the Russian news agency Interfax.

In a statement the ministry said that two crew members and three officers had been on board and it was attempting to ascertain their fate. The Kremlin subsequently said that all five were dead.

International organisations have warned that the shift in the balance of power in Aleppo could serve only to intensify a bloody stalemate in the area where thousands are at risk of starvation. The UN's special envoy to Syria, Staffan de Mistura, warned on 29 August supplies in the east of the city could run out in three weeks.

Civilians continue to pay a heavy price for the fighting. Reports on social media have claimed one student was killed and 13 others wounded after rockets fired by rebel forces landed on the science faculty at Aleppo University.