Teribus . The convention referred to is the one signed by the USA upon which it currently bases the charges against the Syrian regime . Had the Russians supplied Assad with sarin gas without the means of delivering it to the Damscus suburb of Ghouta , the US would correctly be able to charge Russsia with supplying a chemical weapon to the Syrian regime.

Here's a blue clicky to the link ,btw

http://www.opcw.org/about-chemical-weapons/what-is-a-chemical-weapon/