On March 4, former Russian double agent Sergei Skripal and his 33-year-old daughter were found slumped on a bench outside a shopping center in the British town of Salisbury. Authorities said both were in a critical condition after being exposed to an "unknown substance." Skripal was a former general of Russian military intelligence who had been convicted in Russia for spying for the UK.

Russia denied any knowledge of the poisoning, which echoed the murder of former Russian spy Alexander Litvinenko in 2006. Litvinenko was poisoned with radioactive polonium-210. "We see that such a tragic situation happened," Russian President Vladimir Putin’s spokesman Dmitry Peskov told journalists on March 6. "But we don't have information about what could be the cause, what this person did."

On March 7, British police said they suspected a very rare nerve agent was behind the poisoning of Skripal. "This is being treated as a major incident involving attempted murder by administration of a nerve agent," Metropolitan Police assistant commissioner Mark Rowley said in a statement. "I can also confirm that we believe the two people originally who became unwell were targeted specifically."

British police said more than 21 people had sought medical treatment as a result of the nerve agent attack. On March 8, UK Home Secretary Amber Rudd told the House of Commons that enormous resources were being used to determine who was behind the attack. Rudd called the use of a chemical nerve agent on British soil a "brazen and reckless" act that would be answered with all possible force.

On March 12, British Prime Minister Theresa May told lawmakers it was "highly likely" Russia was behind the poisoning. May said the Russian government had either ordered the attack or lost control of the Russian-produced chemical nerve agent Novichok. She gave Moscow until midnight on Tuesday to explain its Novichok program to the Organization for the Prohibition of Chemical Weapons.

On March 13, vice president of the European Commission European Union, Valdis Dombrovskis, said the EU would stand in solidarity with Britain after London accused Russia of being behind the nerve agent attack. When asked if the EU might impose sanctions of Russia if it was agreed Moscow was responsible for the attack, Dombrovskis said: "Of course, the UK can count on EU solidarity in this regard."

Russia failed to respond to May’s midnight deadline for an explanation of its suspected involvement in the poisoning. On March 14, a spokesperson for the Russian Embassy in London said Moscow would not respond "until it receives samples of the chemical substance." May had said a "full range" of retaliatory measures would be considered if Moscow did not give a "credible response" by the deadline.

After Russia failed to give an explanation, May announced on March 14 that the UK would expel 23 Russian diplomats identified as "undeclared intelligence officers." May also said the UK would suspend all high-level bilateral contact with Russia. The biggest expulsions from London in 30 years would "fundamentally degrade Russian intelligence capability for years to come," May said.

On March 15, the leaders of France, Germany, the UK and US released a joint statement that demanded "complete disclosure" from Russia saying there is "no plausible alternative" to Moscow's involvement. The statement said the attack using "a military-grade nerve agent, of a type developed by Russia" constituted "an assault on UK sovereignty" that threatened "the security of us all."

In retaliation to the UK, Russia said it would also expel 23 British diplomats, giving them the same one-week deadline. Russia’s Foreign Ministry said it would also close the British Council in Russia, and might take further measures against Britain in the event of more "hostile steps" from London. Foreign Minister Sergey Lavrov, had said Moscow would "of course" respond with expulsions.

"It's complete drivel, rubbish, nonsense that somebody in Russia would allow themselves to do such a thing ahead of elections and the World Cup," Putin said on March 19. "It's quite obvious that if it were a military-grade nerve agent, people would have died on the spot." Putin said Moscow "destroyed all our chemical weapons under international oversight unlike some of our partners."

On March 20, UK scientists determined Skripal was poisoned using a little-known nerve agent from a group of chemical compounds known as Novichok. The family of compounds, which were developed in the 1970s and 80s, comprise numerous nerve agents. The Soviets once developed these weapons to circumvent the Chemical Weapons Convention. Novichok-5 and Novichok-7 are supposed to be the most dangerous.

A number of EU countries teamed together on March 26 and simultaneously announced they would be expelling Russian diplomats. Germany, France, Poland, Italy, Denmark, the Netherlands, Latvia and Ukraine all announced they would be expelling Russian envoys. The US followed suit with the expulsion of 60 Russian diplomats and announced the closure of Moscow's consulate in Seattle.

UK police found the highest concentration of the nerve agent on the front door of the Skripal's family home in Salisbury. They believe that is where Skripal and his daughter must have first come into contact with the poison. It was likely mixed in with a "gloopy substance" smeared on the door handle.

In early July, weeks after both Skripals were discharged from the Salisbury hospital, another two people were apparently poisoned with the same substance in the nearby town of Amesbury. A 45-year-old man and a 44-year-old woman were found unconscious and were transported to the same hospital in critical condition.

Russian opposition leader Alexei Navalny was rushed to hospital in Siberia after being taken ill on a flight to Moscow. His aides allege he was poisoned in revenge for his campaigns against corruption. The 44-year-old ex-lawyer apparently only drank black tea before taking off from Omsk airport, which his team think was laced with a toxin that put him in a coma.

In 2018, Russian-Canadian activist Pyotr Verzilov was reported to be in a critical condition after allegedly being poisoned in Moscow. It happened shortly after he gave a TV interview criticizing Russia's legal system. Verzilov, the unofficial spokesman for the rock group Pussy Riot, was transferred to a hospital in Berlin where doctors said it was "highly probable" that he had been poisoned.

Sergei Skripal, a 66-year-old former Russian spy, was found unconscious on a bench outside a shopping center in the British city of Salisbury after he was exposed to what was later revealed to be the nerve agent Novichok. Russian President Vladimir Putin’s spokesman Dmitry Peskov called the situation "tragic" but said, "We don't have information about what could be the cause" of the incident.

The estranged half-brother of Kim Jong Un was killed on February 13, 2018 at Kuala Lumpur airport after two women allegedly smeared the chemical nerve agent VX on his face. In February, a Malaysian court heard that Kim Jong Nam had been carrying a dozen vials of antidote for the deadly nerve agent VX in his backpack at the time of the poisoning.

Former Russian spy Litvinenko had worked for the Federal Security Service (FSB) before he defected to Britain, where he became a journalist and wrote two books of accusations against the FSB and Putin. He became ill after meeting with two former KGB officers and died on November 23, 2006. A government inquiry found he was killed by radioactive polonium-210 which it alleged the men put in his tea.

In November 2010, doctors at Berlin's Charité hospital discovered high levels of mercury had been found in a Russian dissident couple working in Berlin. Kalashnikov, a freelance journalist and former KGB colonel, had 3.7 micrograms of mercury per litre of blood, while his wife had 56 micrograms. A safe level is 1-3 micrograms. Viktor reportedly told German magazine Focus that "Moscow poisoned us."

Ukrainian opposition leader Yushchenko became sick in September 2004 and was diagnosed with acute pancreatis caused by a viral infection and chemical substances. The illness resulted in facial disfigurement, with pockmarks, bloating and jaundice. Doctors said the changes to his face were from chloracne, which is a result of dioxin poisoning. Yushchenko claimed government agents poisoned him.

On September 25, 1997, Israel's intelligence agency attempted to assassinate Hamas leader Meshaal, under orders from Prime Minister Benjamin Netanyahu. Two agents sprayed a poisonous substance into Meshaal's ear as he walked into the Hamas offices in Amman, Jordan. The assassination attempt was unsuccessful and not long afterward the two Israeli agents were captured.

In 1978, Bulgarian dissident Markov was waiting at a bus stop after a shift at the BBC when he felt a sharp jab in his thigh. He turned to see a man picking up an umbrella. A small bump appeared where he felt the jab and four days later he died. An autopsy found he'd been killed by a small pellet containing a 0.2-milligram dose of ricin. Many believe the poisoned dart was fired from the umbrella.

On December 30, 1916, mystic and spiritual healer Rasputin arrived at Yusupov Palace in St Petersburg at the invitation Prince Felix Yusupov. There, Prince Yusupov offered Rasputin cakes laced with potassium cyanide but he just kept eating them. Yusupov then gave him wine in a cyanide-laced wine glasses, but still Rasputin continued to drink. With the poison failing, Rasputin was shot and killed.