Russian warplanes struck a marketplace in Khan Sheikhun town in northwestern Idlib province, local journalist Hamid al-Qatini told Anadolu Agency.
"Four people, including a child, were killed and six others injured in the attack," he said.
Local teams were looking for victims under the debris of destroyed buildings in the area, Qatini added.
Khan Sheikhun was the scene of a sarin gas attack earlier this month which left around 100 people dead and hundreds injured.
Meanwhile, five civilians were killed by airstrikes and artillery fire launched by Syrian regime forces on the opposition-held town of Al-Hula in Homs province.
Syria has been locked in civil war since early 2011, when Bashar al-Assad's regime cracked down on pro-democracy protests. According to the UN envoy to Syria, at least 400,000 people have been killed and millions displaced.
