The exodus is expected to continue, with thousands of people on the move as whole towns and communities flee to the safety of areas near the Turkish border, David Swanson told Reuters.
"Tragically, the number of people displaced ‐ the vast majority of them women and children ‐ has now surpassed 800,000," Swanson said.
Russian jets and Syrian artillery have pounded towns and villages since early December in a renewed assault backed by pro-Iranian militias and aimed at clearing the opposition.
"Residents are fleeing by the thousands in open trucks or by foot; often at night to escape detection despite the bitter cold temperatures," Swanson, the U.N. regional spokesman for Syria, told Reuters.
U.N. officials say the region is on the brink of a humanitarian catastrophe. Those on the run in Idlib and adjoining Aleppo province are joining close to 400,000 people who fled earlier bouts of fighting to the safety of camps near the Turkish border.
The latest offensive has brought the military campaign closer to heavily populated northern Idlib along the border, where nearly 3 million people are trapped, according to the United Nations.