The nerve agent used to poison former Russian spy Sergei Skripal and his daughter, Yulia, in an English town was delivered in a liquid form, the British Department for Environment, Food and Rural Affairs (DEFRA) said on Tuesday.
A very small amount of the novichok nerve agent was used in the attack and the highest concentration was found at Skripal's house, the Department revealed.
Nine sites have been identified as needing some sort of specialist cleaning, Defra said.
The sites include part of the Maltings shopping centre where Skripal and Yulia collapsed on April 4, the Zizzi restaurant and Mill pub which they visited that day, and the family home on the outskirts of Salisbury.
The home of the police officer injured in the incident also needs decontaminating, the Department said.
Last week, previously classified intelligence about the Salisbury attack claimed Russia had tested whether door handles could be used to deliver nerve agents.
A small cordoned area of the cemetery where the bodies of Skripal's wife and son lie has been reopened after "extensive investigations and testing" established that it was not contaminated.
The other nine potentially contaminated sites will remain secured.
Work to clean each site will involve a process of testing, removal of items which may have been contaminated, chemical cleaning and retesting.
Sites will not be released back into use until the test results and the work undertaken has been reviewed and approved by the government's decontamination science assurance group.
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