The Syrian Observatory for Human Rights described as a "massacre" the strikes on a vegetable market in Maaret al-Numan that killed at least 37 civilians and at least another seven at a fish market in nearby Kafranbel.
Previously, the Britain-based monitor had put the toll in Maaret al-Numan at five dead and dozens wounded.
The two locations, both in Idlib province, are only about 10 kilometres (six miles) apart.
Both under the control of Al-Qaeda's Syrian offshoot Al-Nusra Front, which like the jihadist Islamic State group is excluded from a ceasefire agreed between mainstream rebels and the regime of President Bashar al-Assad.
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In Damascus province, at least seven people were killed and 10 wounded in strikes on Bala, in the rebel-stronghold region of Eastern Ghouta, the monitor added.
And fighting continued between rebels and regime forces in Latakia province, an Assad stronghold, after an alliance of opposition armed groups launched a joint offensive over the regime's truce "violations".
A ceasefire deal agreed between the United States and Russia, which came into effect in February, excludes areas controlled by Al-Nusra and the Islamic State group.
Syria's main opposition group said yesterday it was suspending its official participation in UN-brokered peace talks in Geneva over what it said was the government's repeated "violations" of the truce.