After largely ignoring the rise of the al-Qaida splinter group over the past year, President Bashar Assad's air force has begun to target Islamic State militants more regularly since the extremist faction seized control of much of northern Syria and a large part of neighboring Iraq in June.
Two activist groups, the Aleppo Media Center and the Syrian Observatory for Human Rights, said today's air raids struck the town of al-Bab in Aleppo province.
It was not possible to reconcile the difference in casualty figures, but numbers frequently vary in the chaotic aftermath immediately following attacks.
The strike on the market left scenes of carnage. In one amateur video posted online, civil defense workers scamper around charred hulks of bombed-out cars and trucks. Three bodies, their limbs at odd angles, lie in a pool of blood. The fluffy coat of crushed sheep can be seen in the back of one half-smashed truck.
More From This Section
Al-Bab is one of the Islamic State group's strongholds in Aleppo province, where the extremists have been chipping away at territory long-held by Syria's mainstream rebels.
The beleaguered mainstream armed opposition has largely been on the losing end of a bloody nine-month battle with the Islamic State group across northern Syria.
But those rebels, who also are fighting Assad, received a long-awaited boost yesterday when President Barack Obama said he would authorize US airstrikes inside Syria for the first time. Such strikes, along with an expanded aerial campaign in Iraq, are part of what Obama called "a steady, relentless effort" to root out and ultimately defeat Islamic State extremists.