A man in his 60s and a women in her 30s remain in a critical, but stable condition in intensive care after being exposed to a nerve agent.
Moscow, not only disputed the nationality of the spy but went a mile more claiming that he was attacked by the British counter-intelligence MI5, instead of British claims that Skirpal and his daughter were poisoned by nerve agents.
Around 180 troops, including Royal Marines, RAF and chemical specialists, are understood to have been deployed.
One hundred military personnel with expertise in dealing with chemicals have been sent to Salisbury to investigate the source of the nerve agent that struck down a Russian former double agent and his daughter.
It is thought their deaths are forming part of the Met Police Counter Terror team's investigations into the attack on Mr Skripal, 66, and his daughter Yulia, 33, on Sunday.
A police officer who responded to the incident is in hospital.
However, the Associated Press quotes the Wiltshire county acting police chief as saying that "around 21 people" have been treated and that "a number" received "blood tests, support and advice".
Hundreds of investigators, led by counter-terror police, are working to find out who is responsible for what is feared to be a sophisticated plot amid heightened tensions between Britain and Russian Federation.
There is also a cordon around the graves of Mr Skripal's son, Alexandr, and his wife, Lyudmila, who died in suspicious circumstances in 2017 and 2012 respectively.
Britain's chief medical officer, Sally Davies, said on March 8 that the general public was not necessarily at high risk, but experts said nerve agents are unsafe and extremely volatile.
Investigators wearing hazmat suits have been seen searching Sergei Skripal's house and vehicle for evidence, and parts of Salisbury city centre near where the victims collapsed remain cordoned off.
Britain has said it will respond robustly if evidence shows Russian Federation was behind the attempted murder.
During the attempted poisoning of former Russian intelligence officer Sergei Skripal in the British city of Salisbury, injured 20 people, including the daughter of Yulia Skripal and Sergeant nick Bailey.
Foreign Secretary Boris Johnson said ministers, officials and dignitaries may not attend the event if there is evidence of state involvement in the incident.
The attempted murder of Mr Skripal has drawn comparisons to the 2006 assassination of Alexander Litvinenko, who ingested the rare and highly radioactive Polonium 210 in London.
"Of course we should exercise caution before jumping to any conclusions but, whoever is responsible - and there are not 101 likely offenders - this is an outrageous affront to our security in Europe and our way of life", said Rob Wainwright, executive director of Europol and a former MI5 analyst.
Russian Foreign Minister Sergey Lavrov said Moscow might be willing to help with the investigation but expressed resentment at suggestions the Kremlin was behind the attack. However, their condition is not so serious.
Blair, the former London police chief, called for a review of the deaths of 14 Russians in the United Kingdom amid suggestions they were targeted by the Russian state.
Colonel Skripal was convicted of treason in 2006 and jailed for 13 years for selling secrets to MI6, which had recruited him in the 1990s.
After a communication breakdown this week with the U.S. State Department, the Russian Embassy in Washington proposed using Twitter for diplomatic correspondence.
It is known that Mr Skripal and his daughter had visited the Mill pub and Zizzi restaurant in Salisbury on Sunday afternoon, before they were found near the Maltings shopping centre.
Skripal has been living in Britain since 2010, when he was part of a prisoner exchange for 10 Russian spies arrested by the Federal Bureau of Investigation.
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