The Syrian Observatory for Human Rights said the raids hit a square in the town of Al-Janudiyah, in the west of the province, which is now almost completely controlled by opposition forces.
"It's a public square, and a lot of people gather there because there are shops," said Observatory director Rami Abdel Rahman.
He told AFP that people displaced from other areas of Idlib province had also sought refuge in Al-Janudiyah.
Al-Janudiyah has been under opposition control for some time, but much of the province has only recently fallen to a rebel alliance that includes Al-Qaeda affiliate Al-Nusra Front.
Al-Janudiyah lies north of Jisr al-Shughur, which fell on April 25, less than a month after the alliance seized the provincial capital Idlib city.
Government forces now hold only a handful of positions in the province.