At least 11 civilians were killed and dozens more wounded on Saturday in air strikes on a central Syrian village that a monitor said were likely carried out by Russia.
"The raids targeted a livestock market in the village of Oqayrabat, held by the Islamic State group in Hama province," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
"They are probably Russian air strikes," he said, adding that 45 people were also wounded.
Oqayrabat lies northwest of Palmyra, the ancient desert city that was recaptured by Russian-backed government forces from IS on Wednesday.
The road between the two had been often used by jihadists to travel between the provinces of Hama and Homs, where Palmyra lies.
Abdel Rahman said the raids on the village were part of "new military operations by the Syrian regime and its Russian ally targeting jihadist positions in Hama province".
Syrian and Russian warplanes on Saturday were heavily bombing IS jihadists north and east of Palmyra, which has changed hands several times in Syria`s nearly six-year war.
IS overran the city for the second time on December 11.
A day later, 53 civilians were killed in a barrage of raids on Oqayrabat and other nearby villages, according to the Observatory.
The Organisation for the Prohibition of Chemical Weapons (OPCW) also raised fears at the time that chemical weapons may have been used in air strikes on Oqayrabat.
The Observatory, which relies on a network of sources inside Syria for its information, says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.
Tens of thousands of Syrian civilians have fled ferocious fighting between Russian-backed regime forces and Islamic State group jihadists over the past week in the country's ravaged north.
Supported by Russian air power and artillery, Syrian government forces have waged a fierce offensive against IS, seizing around 90 villages since mid-January.