Air strikes on a village in Syria's rebel-held Idlib province killed at least 44 people overnight, the highest death toll in a single attack on the region this year, the Syrian Observatory for Human Rights said on Friday.
The monitoring group said Russian war planes probably carried out the attacks. The Russian Defense Ministry later denied its war planes were involved, according to Russian news agencies.
Russia is Syrian President Bashar al-Assad's main ally in his war against an armed opposition, now in its seventh year.
The Observatory said the jets targeted the village of Zardana in northern rural Idlib overnight, killing 27 men, 11 women and six children.
The death toll is expected to increase, since some of the 60 injured in the strikes were in a critical condition, the Britain-based Observatory said. Rescue workers were still searching the rubble for survivors.
The Russian ministry was quoted as saying it had information about fighting between Nusra Front militants and opposition fighters involving heavy artillery fire in the past 24 hours.
The Observatory had reported on Wednesday night violent clashes in the village between local factions, but later said the destruction and resulting casualties were due to air strikes.
Idlib, a region in northwestern Syria, remains the largest populated area of the country in the hands of insurgents fighting the Damascus government.
In recent years, tens of thousands of fighters and civilians have fled there from parts of the country the army has recaptured with the help of Russia and Iran.