Al Jazeera Suhaib al-Khalaf, reporting from Idlib city, Syria, said the overall toll was expected to rise because dozens of people had been wounded or were still missing after the attack.
The UK-based Syrian Observatory for Human Rights said it was not immediately clear whether Monday's attacks on al-Atarib, a town in a so-called de-escalation zone, had been carried out by Syrian or Russian warplanes.
Videos posted on social media purported to show massive destruction at the scene with rubble from damaged buildings covering the town's street and people’s faces drenched in blood.
The air raids come less than two weeks after peace talks in Astana where Russia, Turkey and Iran announced plans to implement no-fly zones over four so-called de-escalation zones.
The zones, which include the provinces of Idlib, Homs, Latakia, Aleppo and Hama - are areas where fighters and government forces should halt hostilities, including air raids, for six months.
More than 2.5 million people are believed to live in the zones.
The agreement, however, excludes the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group and Hay'et Tahrir al-Sham.
Idlib is mainly controlled by Hay'et Tahrir al-Sham, an alliance of anti-government groups formed in January and linked to al-Qaeda.
Syria's conflict evolved from a government crackdown on protests in 2011 to a devastating war that has drawn in world powers, including Russia and a US-led international coalition.
Since then, hundreds of thousands of people have been killed and more than 10 million displaced, according to the UN.