The attempted murder of a former Russian double agent and his daughter on British soil has led to accusations of Russian state involvement.
Soon after the attack on Sergei Skripal, 66, and his 33-year-old daughter, Yulia, in Salisbury, Prime Minister Theresa May said the chemical used had been identified as being part of a group developed by Russia known as Novichok.
The British government went on to expel 23 Russian diplomats and their families after Moscow refused to explain how a Russian-made nerve agent was used in the poisoning.
Twenty-nine countries expelled 145 Russian officials in solidarity with the UK – and Nato ordered 10 Russians out of its mission in Belgium.
Moscow initially responded in kind, expelling 23 British diplomats, 60 US diplomats and several from other countries. It has also closed the British Council in Russia and the British Consulate in St Petersburg.