Humanitarian chief describes as "horrific" the deaths of at least 10 children in air raid by regime forces in Aleppo.

No fewer than 10 children were among 19 people killed in a Syrian regime air raid on a school in Aleppo, an attack described by the UN's humanitarian chief as a horrific violation of law.

According to the UK-based Syrian Observatory for Human Rights, an anti-government monitoring group, Wednesday’s attack hit the Ein Jalout school in the east of the city

Activist videos showed the bodies of the 10 children laid out in a local hospital, wrapped in sheets, and bulldozers removing rubble from the smashed building.

Valerie Amos, the UN's under-secretary general for humanitarian affairs, said she was appalled by the attack.

"It's absolutley horrific what is happening day by day children, women, men, being directly targeted," she said. "It's a flagrant violation of the basic tenants of war."

The UN also said the security council resolution to provide humanitarian aid, passed two months ago, was not working.

"The humanitarian situation in Syria is beyond catastrophic. More than two months after a UN resolution to alleviate the suffering of civilians and end war crimes was adopted, the situation there has only worsened," said Jose Luis Diaz, from the UN office in New York.

Thousands of Syrian children have died in the three-year conflict, which began as an uprising against President Bashar al-Assad's rule and has now become a civil war in which more than 150,000 people have died and millions have been displaced.

Aleppo has borne the brunt of the violence.

Forces loyal to Assad have carried out air raids and dropped crude barrel bombs in rebel-held districts in the eastern part of the city, at times hitting schools, mosques and markets.

The air raid follows a mortar bomb attack and double car-bombing on Wednesday that killed at least 54 civilians in pro-Assad districts of Homs and Damascus