An air raid on a rebel-held neighbourhood of Syria's main northern city Aleppo hit a school, killing at least 18 people, ten of them children, a monitoring group said.

At least one teacher was also among the dead in the raid today on the Ansari district of the former commercial hub, the Syrian Observatory for Human Rights said.

Amateur video distributed by activists in Aleppo showed rows of bodies of children, some of them bloodied, wrapped in grey body bags on the ground.

Aleppo-based citizen journalist Mohammed al-Khatieb told AFP that the children were "holding a drawing exhibition when two air strikes, ten minutes apart, struck the school."

Observatory director Rami Abdel Rahman said most of the children killed were aged 12 or 13.

Rebel-held areas of Aleppo have come under massive assault from the air since mid-December. 

The government's use of barrel bombs, unguided munitions usually dropped from altitude to avoid ground fire, has come in for particular criticism from human rights watchdogs because of their indiscriminate toll on civilians.

The air strikes came a day after at least 100 people, most of them civilians, were killed by twin car bombs claimed by jihadists in a government-held district of Syria's third city Homs.

Al-Qaeda's Syria affiliate, Al-Nusra Front, said it carried out the attack against the city's Abbasiyah neighbourhood, which is mainly inhabited by members of the Alawite minority community of Syrian President Bashar al-Assad.

Yesterday, mortar fire killed 14 people in Damascus, the state SANA news agency reported, blaming rebels in the outskirts of the capital.