UN's Syria peace envoy, Staffan de Mistura, has offered to personally travel to Idlib to help ensure civilians can leave through a humanitarian corridor amid fears of full-scale military operations in Idlib.

"I am once again prepared ... personally and physically to get involved myself, with the government cooperation this time... to ensure such a temporary corridor would be feasible and guaranteed for the people so that they can then return to their own places once this is over," Staffan de Mistura said during a press conference in Geneva.

The UN envoy also called on Russia, Iran and Turkey to hold a possible operation in Syria's Idlib province which would affect millions of civilians.

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".