DAMASCUS, Aug. 13 -- At least 51 people were killed Saturday as a result of rebels' shelling and airstrikes in Syria's northern city of Aleppo, a monitor group reported.

Four children and six women were among those killed by rebels' shelling on government-controlled areas and Syrian airstrikes on rebel-held districts, according to the Syrian Observatory for Human Rights.

The UK-based watchdog group said 15 people were killed by Syrian airstrikes on the rebel-held districts of Fardus, Wajr al-Haj and others in the rebel-held areas in eastern Aleppo.

It added that another 27 people were killed in airstrikes in the western countryside of Aleppo.

In the government-controlled areas west of Aleppo city, nine people including a child and an old man were killed when mortar shells struck residential areas in the Salahuddien district in Aleppo.

Meanwhile, state news agency SANA confirmed that nine people were killed and 20 others wounded in renewed rebel shelling on western Aleppo.

Aleppo, Syria's largest province and once a thriving economic metropolis, has witnessed intensified violent battles lately as both warring parties have stepped up their game in the hope of achieving more gains in that key province.