But during Vladimir Putin’s rule, Western governments have repeatedly accused Russia of using banned chemical substances to assassinate critics, including several times since 2017. The Kremlin denies poisoning opponents.

The State Centre for Research on Virology and Biotechnology in Koltsovo, Siberia, is a former secret Soviet chemical weapons facility that is now one of Russia’s main disease research centres. 

The research facility, also known as Vector, develops vaccines and is one of two sites worldwide known to hold the smallpox virus. It also holds Ebola, bird flu, and hepatitis strains. 

An explosion and fire at the site in 2019 raised fears that it could have accidentally leaked pathogens. The centre insisted there was no biological threat following the incident. Skeptics pointed out that the Soviets had covered up past escapes of anthrax and smallpox from weapons labs in the 1970s. 

In 2004 a researcher at Vector died after accidentally pricking herself with a needle containing the ebola virus.

These are five incidents in which Russia has been linked to chemical weapon use:

The Skripals and the Salisbury poisonings

Britain accused Russia of using nerve agents to poison a former Russian intelligence officer and his daughter in Salisbury in 2018.

Sergei Skripal worked as a double agent for British intelligence during the 1990s and early 2000s before being arrested by Moscow and sent to the UK in a prisoner swap.

Skripal and his daughter, Yulia, spent weeks in intensive care after being poisoned with what the Porton Down military research centre identified as Novichok, a nerve agent the Soviets developed during the Cold War.