Syrian rebels launched a major assault on Friday aimed at breaking a months-long siege of opposition-held districts of Aleppo, as the Assad regime's ally Russia did not renew air strikes.
Fierce fighting, shelling and car bombs that rocked the northern city killed at least 18 regime forces and allied fighters, according to the Syrian Observatory for Human Rights, but it was unable to provide a toll for the rebels.
Once Syria's economic powerhouse, Aleppo has been ravaged by the conflict that began in March 2011 with anti-government protests and has since killed more than 300,000 people.
Control of the city, divided between the rebel-held east and the west in the hands of President Bashar al-Assad's forces, is key to securing northern Syria.
Friday's rebel assault comes more than three months into a government siege of eastern Aleppo, where more than 250,000 people live, and several weeks after the army began an operation to retake the rebel-held east.
Rebel groups "announced the start of the battle to break the siege of Aleppo", said Abu Yusef Muhajir, a military commander and spokesman for the Ahrar al-Sham faction.
The assault "will end the regime occupation of western Aleppo and break the siege on the people trapped inside", he told AFP.
Rebel groups now control "most" of the vast neighbourhood of Dahiyet al-Assad, southwest of Aleppo, with the exception of an area close to a military academy, according to the Britain-based Observatory.
Late on Friday clashes were continuing in the west and southwest of Aleppo, but had decreased in intensity, according to an AFP correspondent in the rebel areas.
Moscow says it has not bombed Aleppo since 18 October but the Russian military said on Friday it had asked President Vladimir Putin for authorisation to resume air strikes.
But Kremlin spokesman Dmitry Peskov said Putin "considers it inappropriate at the current moment", adding the president thought it necessary to "continue the humanitarian pause" in the war-ravaged city.
Despite Russian air support, the Syrian regime has had limited success in its attempts to seize the whole of Aleppo.
The United States on Friday accused the regime of using starvation as a weapon of war - a war crime under the Geneva Conventions - stepping up the rhetoric against Assad and his Russian backers.
Rejecting Kremlin claims that attacks on Aleppo have stopped, a US official told AFP," the regime has rejected UN requests to deliver aid to eastern Aleppo - using starvation as a weapon of war".
Last week, Russia implemented a three-day "humanitarian truce" intended to allow civilians and surrendering rebels to leave the east.
But few did so, and a UN plan to evacuate the wounded failed because security could not be guaranteed.
As the rebels launched their major assault, the Observatory said at least 15 civilians, including a woman and two children, had been killed, and more than 100 wounded in rebel fire on western Aleppo.
The monitor reported fierce clashes on multiple fronts on the western and southern outskirts of west Aleppo, with three suicide car bombs targeting a checkpoint in the Dahiyet al-Assad neighbourhood.