The Syrian army launched an all-out assault on Aleppo's southwestern district of Salaheddin on Wednesday, and fierce fighting also broke out elsewhere in the northern city.

At least 37 people -- 17 civilians, 10 rebels and 10 soldiers -- were killed in the northern city, out of a total of at least 162 people killed across the country, the Syrian Observatory for Human Rights said.

Observatory director Rami Abdel Rahman said it was difficult, because of the ferocity of the clashes, to immediately document the number of people killed in commercial capital Aleppo, and added that the real number would be higher.

The Britain-based watchdog said that of those killed across Syria, 94 were civilians, 41 were regime troops and 27 were rebels.

Among the dead were a woman and her two children killed when a shell hit their house in Aleppo's Al-Mashatiyah neighbourhood, said the watchdog.

The Qatarji, Tariq al-Bab and Shaar neighbourhoods also came under heavy shellfire, it said.

Elsewhere, seven people were killed in the central province of Homs, including a nurse who died when troops shelled the village of Zaafarana.

But the province that suffered the highest death toll was Deir Ezzor in the east, whose eponymous capital has suffered heavy shelling for almost two months, activists say.

The Observatory said 225 people were killed across the country on Tuesday, one of the highest tolls in the nearly 17-month revolt -- 129 civilians, 50 rebels and 46 soldiers.

It is impossible to verify these figures, and the United Nations has stopped maintaining an independent toll. (AFP)