An air strike hit the biggest market on the rebel-held side of Syria's Aleppo on Wednesday, killing at least 15 people.
The strike came as rescuers were still sifting through the rubble from air raids that killed dozens the day before.
Activists said the early afternoon strike destroyed several shops in the besieged eastern part of the city, which has been the target of a massive Russian-backed Syrian offensive since the collapse of a ceasefire last month.
The latest strikes have shattered a relative three-day lull in the area, where hospitals, underground shelters and buildings had been targeted for weeks.
On Tuesday, Russian or Syrian aircraft bombed several neighbourhoods, killing at least 41 people, including five children, according to the Syrian Civil Defence, a group of volunteer first responders, and the activist-run Aleppo Media Centre. Both groups said 15 people were killed in Wednesday's strike.
The Britain-based Syrian Observatory for Human Rights, which relies on a network of contacts in Syria, gave lower tolls for the attacks but said they were likely to rise. Varying reports of casualties are common in the chaotic aftermath of attacks in Syria.
The Observatory said at least 358 civilians have been killed in eastern Aleppo since a US and Russian-brokered truce collapsed on September 19. The UN says over 100 children have been killed in the campaign, which has also included a limited ground offensive.
Syria Civil Defence workers pulled at least one boy alive from under the rubble on Tuesday, amid cheers from onlookers. The 13-year-old, Jamil Habboush, emerged covered in dust and dazed from the flattened building, gripping his rescuer tightly.
His mother survived but remains in critical condition, said Ibrahim al-Haj, a member of the Syrian Civil Defence, which is also known as the White Helmets. The boy had lost his father and brother in previous bombings, according to al-Haj.
The UN Security Council is deadlocked over how to respond to the Aleppo crisis.
The US and Russia have failed to reach an agreement on renewing the short-lived ceasefire. International aid groups and UN agencies have appealed for a halt to the violence to allow aid into the besieged territory. No assistance has entered Aleppo since July, while hospitals, medical facilities and rescue vehicles have all come under attack.