The White Helmets, also known as Syria Civil Defence, said the attacks hit the town of Bidama and three villages –Maasaran, Tal Minnis and Kanayes – in Idlib province.
Death toll from air strikes and artillery attacks on the de-escalation zone in northwestern Syria climbed to 23 on Wednesday, Syrian Observatory for Human Rights said.
Tuesday's attacks by Bashar al Assad's regime hit the town of Bidama and three villages – Maasaran, Tal Minnis and Kanayes – in Idlib province, said the White Helmets, a civil defence agency.
Many others were wounded in the attacks and the number of death toll included children.
The attacks have forced civilians to flee their homes to relatively safer areas near the Turkish border.
Since Moscow and Ankara reached a deal in September 2018, over 1,300 civilians have been killed in the Idlib de-escalation zone.
Over a million Syrians have moved near the Turkish border following intense attacks.
Since the eruption of the bloody civil war in Syria in 2011, Turkey has taken in over 3.6 million Syrians who fled their country, making Turkey the world’s top refugee-hosting country.
Six members of one family killed
Six members of the same family were killed on Tuesday in shelling of the village of Bdama, while four others died in an air strike in the village of Maasaran, both in Idlib province, according to Idlib-based activist Hadi Abdullah and the Britain-based Syrian Observatory for Human Rights (SOHR).
The observatory and Abdullah said another civilian was killed in an attack by helicopter gunships on the village of Talmanas.
In August, after weeks of intense fighting, Syrian troops captured the town of Khan Sheikhoun in Idlib province.
Just north of Khan Sheikhoun is another major town that's still in rebel hands, Maaret al Numan.
The strategic M5 highway passes through Khan Sheikhoun but remains cut in Maaret al Numan. The route has been closed by the rebels since 2012.
Thousands of Maarat al Numan's residents have fled in recent days amid intense air strikes and shelling.
Syrian regime launched a four-month offensive earlier this year against Idlib, forcing hundreds of thousands of civilians to flee their homes.
A fragile ceasefire halted that advance at the end of August, but in recent weeks, it has repeatedly been violated.