Schoolchildren as young as six among latest Aleppo casualties

Rebel shelling hit a school in the government-held west of the contested city on Sunday.

Meanwhile regime forces continued their indiscriminate bombardment of the rebel-controlled east with a barrel bomb attack killing a family of six.

The relentless strikes mark the fifth day of a concerted push by Assad and his allies to expel rebels and reestablish control over Aleppo.

International concern has been mounting since Damascus began a ferocious assault last Tuesday, using air raids, barrel bombs and artillery fire in a bid to recapture eastern Aleppo.

The bombardment, one of the most intense in the almost six year-old civil war, has taken a heavy toll on civilians.

Two medics told Reuters the al-Baytounji family had suffocated to death because the barrel bomb, which fell in the Sakhour district at about midnight, had been laced with chlorine gas.

The Syrian Observatory for Human Rights, which monitors the war, confirmed the bombing but could not confirm that chlorine gas was used.

Damascus has denied use of the gas, which would contravene the international Chemical Weapons Convention.

Children cry and react after their school was bombed [Getty]

Rebel shelling killed at least eight children, aged from six to 12 years, among 10 deaths in the Saria Hasoun school in al-Farqan district, SOHR and Syrian state television reported.

The bombardment of eastern Aleppo drew condemnation on Sunday from the EU's humanitarian aid commissioner Christos Stylianides.

"The relentless bombing of East Aleppo by the Syrian regime in the last few days has now left hundreds of thousands of besieged civilians without access to food and to functioning hospitals," he said.

The World Health Organisation reported on Saturday that bombing had put all hospitals out of action.

Despite warnings of a humanitarian catastrophe without more aid reaching some 250,000 besieged civilians, the Syrian government has rejected a UN truce proposal.