Three women were among those killed in the artillery fire on Al-Bab, which Turkish-backed Syrian rebels have been fighting to take from the Islamic State group, the Syrian Observatory for Human Rights said.
"In the past 48 hours, Turkish air strikes and shelling have killed 45 civilians, including 18 children and 14 women," Observatory head Rami Abdel Rahman told AFP.
Turkey's state-run Anadolu news agency said the army had hit dozens of IS positions, seven of them from the air.
Ankara began military operations in Syria in August last year, targeting Kurdish fighters as well as IS, but says it is doing its utmost to avoid civilian casualties.
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Al-Bab is IS's last stronghold in Aleppo province and has come under fierce attack in recent months by Turkish forces and allied Syrian rebels.
They entered the town last the weekend and are now engaged in "clean-up" operations, Turkish Defence Minister Fikri Isik said yesterday.
The Observatory, however, said Turkish forces had made little progress since entering the town from the west, and rebels said IS was putting up fierce resistance.
At least one jihadist suicide attacker wounded several rebels and seriously damaged their equipment, Abu Jaafar told AFP.
"Daesh seeks to install itself in civilian and public buildings and use civilians as human shields," rebel spokesman Mahmud Hadi said today.
"They use suicide attacks and they move about through basements and tunnels... They infiltrate in between civilians fleeing the military operations to try and penetrate behind the lines of the rebel factions."
Dozens of civilians have been fleeing Al-Bab on a daily basis, according to the Observatory, leaving newly liberated areas as well as escaping territory still under IS control.
On a road leading to the rebel-held town of Azaz, several fleeing residents had piled their belongings into carts on the back of motorbikes and were driving away.
One man driving a truck told a rebel at a checkpoint that IS fighters had fired at the fleeing civilians.
In Azaz, local authorities welcomed arrivals, some of whom were continuing on to rebel-held territory further west, in Idlib province.