At least 30 civilians were killed in shellfire by Syrian rebel groups advancing in the south-western districts of Aleppo over the last 24 hours, a monitoring group said Tuesday.
Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said those killed included 11 children and seven women in the Hamdaniyeh and Ramousseh neighbourhoods.
The two areas are the main target of a rebel offensive aimed at breaking through into opposition-held eastern Aleppo from the south-west after regime forces captured its last remaining supply route last month, placing it under siege.
The heavy shelling, which continued until morning, came as regime forces overnight counter-attacked and won back some positions, the Britain-based Observatory said.
State media said the Syrian air force carried out several strikes on areas controlled by "terrorists", a term used by the regime to describe rebels.
But opposition figures remained upbeat, with Brita Hagi Hassan, the head of the opposition city council, telling dpa via a Facebook message: "If the rebels continue their push into regime areas in south-western Aleppo..., all of Aleppo will be liberated in one week."
Rebels led by the Fatah al-Sham Front, previously known as the al-Nusra Front until it changed its name and ended its formal affiliation with al-Qaeda terrorist organization last week, launched a major offensive on Aleppo's south-western outskirts Sunday evening.
The rebel forces in the area are separated by only a few kilometres of regime territory from besieged eastern Aleppo.
The Observatory said that planes raided by noon several areas in the Sheikh Saeed and al-Sukari districts, killing at least two and wounding several others.
It added that warplanes also struck Atarib in western Aleppo, killing six people and wounding at least 15 others.
The Observatory said that the second stage of the offensive has been dubbed by rebels "Aleppo's anger."
Riad Kahwaji, Founder and Chief Executive Officer of the Institute for Near East and Gulf Military Analysis, told dpa that the opposition forces have surprised their opponents with the level of resilience they have.
"Despite the fierce offensive by the regime forces supported by Russian air cover and the Iranian-supplied Shiite militias, opposition forces managed to regain the momentum through a surprise counter-offensive from the west and south of Aleppo," Kahwaji said.
He added that the rebels seem to be on the verge of encircling regime forces in some pockets in and around the city.
"Air power can do so little in urban fighting especially if the other side [Russia and the Syrian regime] lacks smart weapons and the Russian airpower is clearly short on effective precision weapons," Kahwaji said.
"I believe the battle of Aleppo is proving way much more difficult than the Iranian-Russian axis had expected; and it will be more costly to them if they keep trying to capture the city," Kahwaji warned.
Both Russia and Iran support Syria's armed forces.