Britain-based Syrian Observatory for Human Rights says the civlians, including two children, were killed on the outskirts of Maaret al Numan town and in the villages of Kansafra and Khan al Subul.
Syrian regime air strikes on the rebel-held northwest killed four civilians, two of them children, on Saturday, a war monitor said, as a two-month flare-up showed no let-up.
The two children were killed in a garage on the edge of the town of Maaret al Numan in Idlib, the Britain-based Syrian Observatory for Human Rights said.
The other two civilians were killed in strikes on the Idlib province villages of Kansafra and Khan al Subul, the Observatory said.
Idlib buffer zone deal
The Idlib region of some three million people is supposed to be protected by a September buffer zone deal, but the militants and rebel-run enclave has come under mounting bombardment by the regime and its ally Russia since late April.
The September deal signed by Russia and Turkey was supposed to set up a buffer zone around the Idlib region, but it was never fully implemented as the militants refused to pull back from the front lines.
Hostilities deepened in January when Hayat Tahrir al Sham, an alliance led by Syria's former al Qaeda affiliate, took over administrative control of the region.
Hundreds killed since April
Since late April, more than 460 civilians have been killed in the regime or Russian bombardment, according to the Observatory.
The violence has forced around 330,000 people to flee their homes and hit 23 health centres, according to the UN.
The war in Syria has killed more than 400,000 people and displaced millions since it erupted in 2011 with the brutal repression of protests against President Bashar al Assad.