AMSTERDAM (Reuters) – British Prime Minister Theresa May said on Monday it was“highly likely” that Moscow was responsible for the poisoning in the English city of Salisbury of a Russian former double agent with Novichok, one of the deadliest chemical weapons ever developed.

Here is a brief overview of Novichok:

* First developed in the former Soviet Union in the 1970s and 1980s, Novichok, or“newcomer”, is a series of highly toxic nerve agents with a slightly different chemical composition than the more commonly known VX and sarin poison gases. Read more.