Some victims of a suspected chemical attack in Syria have symptoms consistent with exposure to a category of chemicals that includes nerve agents, the World Health Organization said Wednesday.

The UN health agency said the attack in Idlib province Tuesday, which killed at least 72 civilians, appeared to have involved chemical weapons, pointing to the "apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death."

"Some cases appear to show additional signs consistent with exposure to organophosphorus chemicals, a category of chemicals that includes nerve agents," it said.