French officials are testing samples brought back from Syria by two journalists who say they witnessed chemical weapons attacks.
The journalists say the attacks were carried out by Syrian Government forces against the rebels and took place on the outskirts of the capital, Damascus, last month.
The reporter and photographer from the French newspaper Le Monde went undercover for two months alongside Syrian rebels.
The pair say they saw battlefield chemical attacks and also talked to doctors and other witnesses.
A report in Le Monde says the photographer suffered blurred vision and respiratory difficulties for four days after an attack on 13 April.
The Syrian Government has denied using chemical weapons.