In Idlib, the Syrian Observatory for Human Rights said 58 people were killed in a series of bombings, including one on a vegetable market, with 13 children among the dead.
Footage showed the corpses of a charred child and other victims being pulled mangled bodies from beneath rubble.
"The market was full of shoppers going to buy presents for their kids, they were all civilians," said Salem Idlibi, a civil
Rebel-held areas have also been attacked in Aleppo, which was hit from the air as fighting continued on the ground.
At least 30 people died when barrel bombs were dropped from army helicopters in the east and further civilian deaths were reported elsewhere in the city and across the province.
Both sides appear to be trying to maximise gains before the cessation of hostilities begins at sundown on Monday, which is the start of the Muslim Eid al Adha holiday.
The Syrian government has told Moscow it is prepared to comply with the deal, and opposition forces have also said they will fulfil the peace plan's requirements if the government demonstrates it is serious about ending the bloodshed.
Syria's moderate Free Syrian Army said they saw little chance of the deal's success, with a spokesman for one of its brigades saying that Damascus and Moscow had not observed the last agreement so were unlikely to observe this one.
"We hope this will be the beginning of the end of the civilians' ordeal," Bassma Kodmani, a leading member of the opposition umbrella group, the High Negotiations Committee, said.
But Captain Abdul Salam Abdul Razak, a spokesman for the rebel Nour al-Din al Zinki Brigades, said the deal would only help the Syrian army to gather forces and send more Iranian-backed fighters into Aleppo.
Truces agreed in the past have collapsed after both sides failed to hold up their ends of the bargain.
If the planned cessation of hostilities holds for seven days, it will be followed by an unlikely military partnership between the US and Russia to target Islamic State and al Qaeda.
"Going after Nusra is not a concession to anybody," US Secretary of State John Kerry said.
"It is profoundly in the interests of the United States to target al Qaeda, to target al Qaeda's affiliate in Syria, which is Nusra, an organisation that is opposed to a peaceful transition, an organisation that is an enemy of the legitimate opposition, an organisation that is currently plotting attacks beyond Syria's borders, including against the United States."
Russian Foreign Minister Sergei Lavrov added: "I want to stress that distinguishing between terrorists and moderate oppositions has been written as a priority into the document that we agreed today."
Washington has been tasked with persuading "moderate" rebels to break away from the Nusra Front and other extremist groups.
Mr Kerry said the deal the was a potential "turning point" in the long-running civil war which has killed as many as 500,000 people and displaced millions of others.
However, he warned the plan could be described as nothing more than an opportunity until it is successfully enforced.
Mr Lavrov said the deal would allow efficient co-operation in the struggle against terrorism, and expand humanitarian access to Syria's worst-hit towns and cities.
Turkey, which made a major military incursion into the north of Syria two weeks ago, said it was preparing aid for Aleppo once the truce was in place.
UK Foreign Secretary Boris Johnson welcomed the plan, adding a call for "all parties to the Syria conflict and all countries with influence upon them to do what is needed to end violence and lift sieges".