Russian-led air strikes killed at least 40 people on Tuesday in northwest Syria in a major army assault backed by Iranian militias to clear out rebels that has sent tens of thousands of people fleeing toward the border with Turkey, residents and rescuers said.They said a family of eight including six children was killed in the rural village of Kfar Taal west of government-controlled Aleppo, while another nine civilians were killed in Maardabseh in the southeast of Idlib province.