Britain has warned of a robust response if Russia fails to explain how a nerve agent developed by the Soviet Union was used in an attack on a former Russian double agent who passed secrets to British intelligence.
Sergei Skripal, 66, and his daughter Yulia, 33, have been in hospital in a critical condition since March 4 when they were found unconscious on a bench outside a shopping centre in the English cathedral city of Salisbury.
Below are some details about the nerve agent and previous incidents in which critics or enemies of Moscow have been victims of poisoning or suspected poisoning, or have cried foul after suddenly falling ill.
British scientists identified the substance that Skripal and his daughter were exposed to as part of the highly-lethal Novichok group of nerve agents developed by the Soviet military in the 1970s and 1980s.
Russia has denied any role in the poisoning and says Britain is whipping up anti-Russian hysteria.
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 poisons.
Novichok agents are believed to be five to 10 times more lethal, although there are no known previous uses. Moscow is not believed to have ever declared Novichok or its ingredients to the Hague-based Organisation for the Prohibition of Chemical Weapons (OPCW), which oversees a treaty banning their use.
The chemical “causes a slowing of the heart and restriction of the airways, leading to death by asphyxiation”, said pharmacology expert Prof. Gary Stephens at the University of Reading. “One of the main reasons these agents are developed is because their component parts are not on the banned list.”
During the Cold War, Georgi Markov, a Bulgarian dissident, was killed with a poison-tipped umbrella. Markov, a writer, journalist and opponent of Bulgaria’s then communist leadership, died on Sept. 11, 1978 after someone fired a ricin-laced pellet into his leg on London’s Waterloo Bridge.
According to accounts of the incident, Markov, who defected to the West in 1969, was waiting for a bus when he felt a sharp sting in his thigh. A stranger fumbled behind him with an umbrella he had dropped and mumbled “sorry” before walking away.
Markov later died of what is believed to be ricin poisoning, for which there is no antidote. Dissidents accused the Soviet KGB of being behind the killing.
Ex-KGB agent Alexander Litvinenko, 43, died after drinking green tea laced with polonium-210, a rare and potent radioactive isotope, at London’s Millennium Hotel.
Russian President Vladimir Putin probably approved the killing, a British inquiry concluded in 2016. The Kremlin has denied involvement.
An inquiry led by a senior British judge found that former KGB bodyguard Andrei Lugovoy and another Russian, Dmitry Kovtun, carried out the killing as part of an operation that he said was probably directed by Russia’s Federal Security Service (FSB), the main heir to the Soviet-era KGB.
An outspoken critic of Putin, Litvinenko fled Russia for Britain six years to the day before he was poisoned.
Alexander Perepilichny, a 44-year-old Russian, was found dead near his luxury home on an exclusive gated estate outside London after he had been out jogging in November 2012.
Perepilichny had sought refuge in Britain in 2009 after helping a Swiss investigation into a Russian money-laundering scheme. His sudden death raised suggestions that he might have been murdered.
British police ruled out foul play despite suspicions he might have been murdered with a rare poison. An inquest into his death has yet to give a definitive conclusion as to how he died.
A pre-inquest hearing heard that traces of a rare and deadly poison from the gelsemium plant had been found in his stomach.
Perepilichny had enjoyed a large bowl of soup containing sorrel, a popular Russian dish. Russia denied involvement.
Viktor Yushchenko, then a Ukrainian opposition leader, was poisoned during the campaign for the 2004 presidential election in which he stood on a pro-western ticket against the current Prime Minister Viktor Yanukovich.
He was poisoned with 1,000 times more dioxin than is normally present in the human body. His face and body were disfigured by the poisoning and he had dozens of operations in the aftermath.
Yushchenko subsequently won the presidency in a re-run poll after Ukraine’s Supreme Court, amid street protests dubbed the “Orange Revolution”, struck down the results of a first vote that gave victory to a pro-Moscow candidate.
He said he was poisoned while having dinner outside Kiev with officials from the Ukrainian security services. Russia denied any involvement.
Vladimir Kara-Murza, a Russian opposition activist, says he believes attempts were made to poison him in 2015 and 2017. A German laboratory later found elevated levels of mercury, copper, manganese and zinc in him, according to medical reports seen by Reuters. Moscow denied involvement.