Buildings were reduced to rubble after an air strike on the rebel-held neighbourhood of al-Kalasa in the northern Syrian city of Aleppo yesterday.

The Syrian army said it was preparing an offensive to retake the whole of Aleppo, as fighting killed 38 civilians in a new blow for a tattered truce that began on Feb 27.

Nearly 200 people have been killed in Aleppo in the past week as rebels pounded government-held neighbourhoods with rocket and artillery fire and the regime hit rebel areas with air raids.

The International Committee of the Red Cross said the violence is pushing people to the brink of a humanitarian disaster.

United Nations envoy Staffan de Mistura said that the ceasefire is "barely alive" and pleaded for urgent action by its co-sponsors, Russia and the United States.