At least 34 civilians were killed on Tuesday in suspected Russian air strikes on two markets in northern Syria, a monitoring group said.
The raids killed 16 civilians at a market for fuel in Idlib province, the Syrian Observatory for Human Rights said.
Another 18 civilians, including four women, were killed after strikes on a market in a village held by the Islamic State militant group in the northern Aleppo province.
The Britain-based Observatory said both tolls were likely to rise as many people were critically wounded.
The monitor relies on a network of sources on the ground to collect its information, and identifies aircraft based on their flight patterns and munitions used.
Russia began its air war in Syria on September 30, conducting air strikes against a range of anti-regime armed groups including US-backed rebels and Islamist militant groups.
ISIS has swept across eastern parts of Aleppo province from its bastion in Raqa, fighting both non-Islamist militant rebels and regime troops along the way.
But the northwestern province of Idlib is controlled by the fiercely anti-ISIS Army of Conquest alliance, led by Islamist militant rival Al-Qaeda affiliate Al-Nusra Front.
More than 250,000 people have died since Syria's conflict erupted in March 2011, and millions have fled their homes in the war-torn country.