The Britain-based Syrian Observatory for Human Rights said four women were among the 12 people killed in shelling and airstrikes on several towns and villages in Idlib and neighbouring Hama province.
"The attacks have been continuously escalating for four days," Observatory head Rami Abdul Rahman told AFP.
An AFP correspondent saw intense bombardment of southern Idlib on Friday, when warplanes dropped bombs that sent huge plumes of grey smoke billowing into the sky.
Idlib and nearby areas have been protected from a massive regime offensive since a September deal inked by Damascus ally Russia and rebel backer Turkey.
But the region, currently harbouring some three million people, has come under increasing bombardment since the jihadist group Hayat Tahrir al-Sham took full control of it in January.
The escalation has killed 200 civilians and displaced nearly 140,000 since February, according to the UN.
Abdul Rahman said shelling and airstrikes in recent days have primarily targeted positions and bases belonging to former al-Qaeda affiliate HTS and other armed groups.
The UN says schools and medical centres have also been hit by the new wave of attacks.
State news agency SANA on Friday said the Syrian army "intensified" operations against HTS in Idlib and Hama, targeting armoured vehicles and rocket launchers.
The AFP correspondent saw vehicles loaded with mattresses, carpets and household appliances leaving villages in southern Idlib en route to areas closer to the Turkish border.
Residents said increased attacks have emptied some villages in southern Idlib of their residents.
"We've all left," said Abu Ali, a 40-year-old man who fled the Idlib village of Kafr Ain four days ago because of bombing.
"No one is left in the village because of the shelling," he told AFP.
The civil war in Syria has killed more than 370,000 people and displaced millions since it began in 2011 with anti-regime protests that sparked a devastating crackdown.
