More than 50 civilians including two children were killed and dozens more wounded on Tuesday in regime air strikes that hit marketplaces in two northwestern Syrian towns, a monitor said.
In the Idlib province, which neighbours Latakia, air strikes on a vegetable market in the town of Maarat al-Numan killed at least 40 people and injured dozens, the monitor, rescue worker and opposition source said.
In the nearby town of Kafr Nubl, 10 people were killed, the sources said.
"The regime is trying to storm the area, with the participation of Russian helicopters and Sukhoi (warplanes)," said Fadi Ahmad, spokesman for the First Coastal rebel group in the area.
The Observatory said fighting had been raging since morning, adding that around 15 air strikes also hit northern areas of Homs province on Tuesday.
Syria's Al Qaeda-affiliate Nusra Front is present across much of Idlib province and recently made inroads into Maaret al Numan.
A cessation deal agreed between the United States and Russia, which came into effect in February, excludes areas controlled by DAESH terrorist organisation and Nusra Front.
The deal, however, has been strained by increased fighting around Aleppo, and in other areas of Syria, where both the regime and its opponents have accused each other of a string of breaches.
Syria's main opposition group said Monday it was suspending its official participation in UN-brokered peace talks in Geneva over what it said was the regime's repeated "violations" of the deal.