The head of the British military facility are analysing the Novichok nerve agent. (File photo)
The head of the British military facility analysing the Novichok nerve agent used to poison Russian spy Sergei Skripal and his daughter said Tuesday it has "not verified the precise source" of the substance.
"We have not identified the precise source, but we have provided the scientific info to government who have then used a number of other sources to piece together the conclusions," Gary Aitkenhead, chief executive of the Porton Down defence laboratory, told Britain's Sky News.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)