Sarin nerve agent was used in an 'incident' at a northern Syrian village in late March, five days before the deadly attack on Khan Sheikhun, the world's chemical watchdog said Wednesday.

"Analysis of samples collected (by the OPCW)... relates to an incident that took place again in the northern part of Syria on the 30th of March this year," the Organisation for the Prohibition of Chemical Weapons' director told AFP in an exclusive interview.

"The results prove the existence of sarin," Ahmet Uzumcu said.