The London-based Syrian Observatory for Human Rights said earlier that a Russian warplane attacked a Syrian village in the rebel-held Idlib province on June 7, killing at least 44 people so far, one of the highest death tolls on the region this year.
Observatory head Rami Abdel Rahman said the toll was rising because more bodies had been found under the rubble of houses destroyed in the airstrikes.
"We are deeply troubled by reports that this was a "double-tap" strike, in which aircraft follow up on an initial attack with a second strike which generally hits rescue workers and others coming to the aid of casualties".
Air strikes in northwestern Syria on Thursday, thought to have been carried out by Russian Federation, killed 44 civilians including five children, according to a Britain-based monitor.
"The airstrikes were carried out by SU-24 Russian fighter jets dispatched from the Latakia airbase", Syrian opposition groups said in a statement.
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Half a dozen men in civilian clothes helped carry a person in a black body bag away from the site of the strikes, which pulverized several buildings. At least 92 extremist fighters were killed during that same period.
IS has ramped up its attacks against pro-regime forces since its fighters in May left their last stronghold near Damascus under an evacuation deal with the regime.
The monitoring group said Russian war planes probably carried out the attacks. He said: "Our troops will stay in Syria as long as it is beneficial to Russia".
Hundreds of thousands of civilians have been killed since the war's outbreak in 2011, mostly by the regime and its powerful allies.