A general view taken with a drone shows part of the rebel-held Idlib city, Syria, June 8, 2017. Photo: Reuters / Ammar Abdullah / File.

The United Nations called on Russia, Iran and Turkey on Thursday to forestall a battle in Syria’s Idlib province which would affect millions of civilians and could see both sides using chlorine as a chemical weapon.

UN Syria envoy Staffan de Mistura told reporters that there was a high concentration of foreign fighters in Idlib, including an estimated 10,000 terrorists, but it would be better to set up humanitarian corridors to evacuate civilians than rush into a battle which could turn prove to be a “perfect storm.”