A young girl was among those killed at a market in the town of Maaret al Numan in Idlib province, the Syrian Observatory for Human Rights said.
Regime air strikes killed 12 civilians including four at a market on Sunday in a militant bastion in northwest Syria, a war monitor said.
Eight other civilians were killed elsewhere by regime fire in Idlib, a stronghold of Syria's former Al Qaeda affiliate Hayat Tahrir al-Sham, the Britain-based monitor said.
Idlib is supposed to be protected from a massive regime offensive by a September buffer zone deal, but the militant bastion has come under increasing bombardment by the Assad's forces and its Russian ally since late April.
An AFP reporter in Maaret al Numan saw a young man carry the arched body of what appeared to be a young girl out over grey rubble after the air strike.
Another man retrieved a distressed, dust-covered young girl, slung over his shoulder.
Witness Hamdu Mustafa said he was out shopping when the air strike hit.
Everybody was "in the street selling and buying," he told AFP.
"The planes targeted civilians who were buying food for their children," he said.
Nearby, rescue workers known as the White Helmets directed a bulldozer to clear the debris.
Fighting has raged to the south of the bastion in recent days.
On Sunday, regime forces took back control of the town of Kafr Nabuda in the north of Hama province, the Observatory and state news agency SANA said.
HTS and allied rebels overran part of the town in recent days after the regime first expelled them on May 8.
The United Nations has warned that an all-out offensive on the Idlib region would lead to a humanitarian catastrophe for its nearly three million residents.
The Observatory says more than 230 civilians have been killed in the spike in violence since the end of April.
More than 200,000 civilians have already been displaced by this upsurge of violence, the United Nations has said.
A total of 20 health facilities have been hit by the escalation – 19 of which remain out of service, according to the UN.