Medical samples of attack victims in Syria have tested positive for the nerve agent sarin, the British and French governments have revealed.
They added that they have shown the evidence to a UN investigation.
According to the Guardian, the Foreign Office confirmed that body fluids collected from victims of one or more attacks in Syria were found to contain a chemical fingerprint of sarin at the Ministry of Defence's Porton Down facility in Wiltshire.
In Paris, French foreign minister, Laurent Fabius, said he had passed similar evidence to the head of the UN inquiry into chemical weapon use in Syria, Ake Sellstrom.
Fabius said that on France's behalf he handed Sellstrom the results of analyses carried out in their laboratory, adding that the analyses demonstrated the presence of sarin gas in the samples in their possession.
In view of this evidence, France is now certain that sarin gas has been used in Syria several times and in a localised manner.
Appearing on French TV news, Fabius said France had no doubt that the gas was used and that in the second case, there was no doubt it was used by the regime.
The Foreign Office also confirmed that physiological samples collected from Syria had tested positive for sarin.
Sarin can be detected in blood and urine if samples are taken soon after an attack, but the chemical is volatile and quickly degrades into other compounds, the report added.
