Jet strikes blamed on the Syrian regime hit the opposition-held cities, killing more than 40 people and wounding 90, hours after the US and Russia announced a deal intended to bring a ceasefire in the war-torn country.
At least 45 people have been killed after intense airstrikes on Saturday on and around the northern rebel-held city of Aleppo, according to opposition activists.
TRT World reported the death count could be over 50.
The Aleppo Media Center, an activist collective, said 45 people were killed on Saturday, just hours after the new US-Russian agreement was reached to try and end the violence in Syria.
The Britain-based Syrian Observatory for Human Rights said 30 people were killed in Aleppo province and another 39 were killed by airstrikes in neighboring Idlib province.
Contrasting casualty figures are common in the aftermath of large attacks in Syria.
The United States and Russia announced a deal Saturday that would establish a nationwide cease-fire starting on Monday.
Earlier, it was reported that airstrikes on Idlib have killed at least 24 people.
The Syrian Observatory for Human Rights also said that more than 90 people might have been wounded in the air strikes – which hit a market place and several other areas of the city – and it was not immediately clear who carried out the strikes.
An Agence France Presse photographer at the scene saw men clambering over rubble, in just slippers or sandals, to help evacuate wounded, dust-covered residents and children from a collapsing building.
Local civil defence personnel told Reuters that bodies were still being removed from the rubble of buildings destroyed in the strikes.
Reuters also reported residents and rescue workers as saying that two dozen people were killed in the strikes, and that Russian jets acting in support of the Bashar al Assad's regime forces – identified as such because they were flying in sorties at a high altitude – may have been responsible.
Since spring 2015, most of Idlib Province has been held by an alliance of rebel groups known as the Army of Conquest.
More than 290,000 people have been killed since the conflict in Syria first erupted in March 2011, and several attempts at securing a long-lasting truce have failed.