A Turkish minister has told his country's media that autopsies prove chemical weapons were used in the attacks on Idlib this week.
More than 70 people were killed in back-to-back attacks on Tuesday and Wednesday in the rebel-held town of Khan Sheikhun.
A large number of the victims were women and children.
The Turkish justice minister Bekir Bozdag stated the results of three autopsy reports from Syrians caught up in the attack, who were brought to Turkey for treatment and later died in hospital.
The state-run Anadolu Agency is reporting a representative from the World Health Organisation witnessed the autopsies.
It says Turkey has confirmed to the United Nations the substance used in the attacks was chlorine gas.