Syrian fighter jets screamed through the sky over a rebel-held town, dropping bombs that levelled the better part of a poor neighbourhood and wounded scores of people, many of them women and children buried under piles of rubble.
The British-based Syrian Observatory for Human Rights said 23 people died in the double air strike and more than 200 were wounded. Mohammed Nour, a local activist reached by phone, put the death toll at 25. Neither figure could be independently confirmed.
Reporters from The Associated Press saw nine dead bodies in the immediate aftermath of the bombings in Azaz, including a baby.
The attacks sent panicked civilians fleeing for cover. So many were wounded that the local hospital locked its doors, directing people to drive to the nearby Turkish border so the injured could be treated on the other side. One person's remains were bundled into a small satchel.
The bombing of Azaz, 30 miles north of Aleppo, shattered the sense of control rebels have sought to project since they took the area from President Bashar Assad's army last month. Azaz is also the town where rebels have been holding 11 Lebanese Shiites they captured in May.
The attack came on the same day the United Nations released a report accusing Assad's forces and pro-government militiamen of war crimes during a May bloodbath in the village of Houla that killed more than 100 civilians, nearly half of them children. It said rebels were also responsible for war crimes in at least three other killings.
The long-awaited report by the UN Human Rights Council marks the first time the world body has referred to events in Syria as war crimes - on both the government and rebel sides - and could be used in future prosecutions against Assad or others. It said the scale of the Houla carnage indicated "involvement at the highest levels" of Syria's military and government. The council also said the conflict was moving in increasingly brutal directions on both sides.
The Organisation of Islamic Co-operation, comprising 57 member states, released a final statement on Wednesday from its two-day summit in Saudi Arabia's Muslim holy city of Mecca, urging support for the opposition.
The statement did not mention suspending Syria's membership, but OIC secretary general Ekmeleddin Ihsanoglu said after the summit that the organisation had agreed to do so. The move is largely symbolic.
Iran's foreign minister Ali Akbar Salehi, whose nation is Assad's most staunch regional supporter, said before the opening session in Saudi Arabia that suspending Syria would not resolve the issue of the unrest.