Syrian Observatory for Human Rights says eight civilians were killed in the town of Saraqeb while four others were killed in separate air strikes in other towns of southern Idlib.
Air strikes by the Syrian regime and its ally Russia on Saturday killed 12 civilians in the country's last major opposition bastion where a rise in violence has forced tens of thousands to flee.
The bombardments hit the northwestern province of Idlib, which has been increasingly targeted this month by regime leader Bashar al Assad's forces.
On Saturday, the bombing killed eight civilians in the town of Saraqeb, according to the Syrian Observatory for Human Rights [or SOHR]
Four others were killed in separate air strikes in other towns in southern Idlib.
And 36 others were wounded, the Britain-based monitoring group added.
The intensification of air strikes on southern Idlib since December 16 has forced tens of thousands to flee their homes, according to the United Nations.
The bombardment came as violent clashes continued for a third straight day between regime loyalists and the opposition forces and rebels who dominate the province.
Battles since Thursday have killed 67 militants and 15 allied rebels, the Observatory said.
Fifty-seven regime loyalists were also killed, bringing the total casualty count to nearly 140 on both sides, it added.
The Idlib region is home to some three million people including many displaced by Syria's civil war.
The Damascus regime has repeatedly vowed to take back control of it from the militants and rebel fighters.
Pro-regime forces launched a blistering offensive against the region in April, killing around 1,000 civilians and displacing more than 400,000 people from their homes.
Since August, the area has supposedly been protected by a ceasefire announced by Moscow, but bombardments have continued.
Syria's war has killed over 400,000 people and displaced millions since beginning in 2011 with the brutal repression of anti-regime protests.