Russian air strikes killed at least 13 people in rebel-held northwest Syria on Sunday, the deadliest attack on the country this year, a war monitor said.
At least nine civilians, including two children, were among the dead, with most killed at a fruit and vegetable market in Jisr al-Shugur in the Idlib region.
"These Russian strikes are the deadliest in Syria this year and amount to a massacre," said Rami Abdel Rahman, who heads the Britain-based Syrian Observatory for Human Rights.
Russian forces which back President Bashar al-Assad's regime were responding to rebel drone strikes over the past week that killed four civilians including two children, according to the Observatory.