United Nations: The UN Security Council will meet Sunday to discuss the escalating violence in Syria’s second city of Aleppo, diplomats said.

The meeting scheduled for 11:00am (1500 GMT) was requested by Britain, France and the United States.

Intense air strikes toppled buildings and killed at least 45 civilians in Aleppo on Saturday, two days after the Syrian army announced an offensive to retake the rebel-held east of the city.

UN Secretary General Ban Ki-moon earlier said he was appalled by the ‘chilling’ upsurge in fighting in Aleppo, and warned that the use of advanced weaponry in the battleground city could amount to war crimes.

Ban cited reports of air strikes involving the use of incendiary weapons, bunker buster bombs and other powerful munitions in the offensive launched by the Syrian army two days ago to recapture the city.

He warned that ‘the apparent systematic use of these types of indiscriminate weapons in densely populated areas may amount to war crimes,’ a statement from his spokesman said.

A weeklong ceasefire agreed between the United States and Russia ended on Monday and efforts to revive the truce failed.