Bombs dropped by suspected Russian warplanes have killed at least 12 Syrian children at a school in a rebel-held town in Aleppo province, the Syrian Observatory for Human Rights says.

The air strike hit the town of Injara some 15 kilometres west of Aleppo city.

A teacher also died and there were reports of others wounded, some critically, the monitor said.

Social media footage released by opposition activists showed a classroom with destroyed benches and textbooks lying on the floor stained with blood.

The footage could not be independently verified.

There was no immediate comment from Moscow, which denies any targeting of civilians in the conflict.

In Geneva, a spokesman for the UN children's fund UNICEF said it was looking into the reports of the raid.

The Kremlin launched air strikes over Syria in September saying it wanted to help President Bashar al-Assad, its main Middle East ally, defeat Islamic State and other militant groups.

Incident casts doubts on peace talks

Syria's opposition coordinator Riad Hijab put the death toll at 35 children and said the Russian strikes had hit three schools in total.

He said such actions meant the opposition could not negotiate with President Bashar al-Assad's government.

"We want to negotiate, but to do that the conditions have to be there," Mr Hijab told reporters after a meeting with French President Francois Hollande.

"We cannot negotiate with the regime when there are foreign forces bombing the Syrian people."

Rescue workers and rights groups say Russia's bombings have killed scores of civilians at busy market places and in residential areas away from the frontlines. Russia denies this.

Amnesty International said last month that Moscow's actions had violated humanitarian law.

US officials said Russia used fewer precision-guided munitions than the United States and its allies.

Reuters