A "very small amount" of the Novichok nerve agent was used in the attack, with the substance delivered in a "liquid form", the Department for Environment, Food and Rural Affairs has said.
The details emerged at a press briefing in Salisbury, where reporters were told the highest concentration was found at Mr Skripal's house.
Clean-up work is set to begin at nine sites across the city, as a tenth, an area of the London Road cemetery - which was found not to be contaminated - will reopen to the public on Tuesday.
"We either know there is contamination there (in the nine sites) or we think there is a probability we could find contamination there," Defra said.
Salisbury residents have been warned to expect a step-up in activity as investigators wearing protective clothes remove items and chemically clean the areas.
ITV News understands that Detective Sergeant Nick Bailey is close to being able to leave Salisbury District Hospital.Read the full story ›
Police have cordoned off a stretch of Hyde Road, in Gillingham, Dorset, and Army personnel and vehicles were pictured entering the cordon on social media.
This follows an incident in Salisbury in which a former Russian spy and daughter where poisoned using a nerve agent.
An recovery vehicle could be seen inside the area.
The military is assisting police to remove a number of vehicles and items from areas of Dorset, following the incident in Salisbury.
The public should not be alarmed and the public health advice remains the same. The military has the expertise and capability to respond to a range of contingencies.
The Ministry of Defence regularly assists the emergency services and local authorities in the UK. Military assistance will continue as necessary during this investigation.
Jamie Knight pleaded guilty to a racially-aggravated public order offence, assaulting a police officer, common assault and criminal damage.Read the full story ›
Emergency workers in hazmat suits were seen examining the graves of Sergei Skripal's wife and son.Read the full story ›
Sergeant Nick Bailey remains in hospital after he came into contact with the nerve agent after going to help Mr Skripal.Read the full story ›
CCTV footage shows Sergei Skripal days before he was exposed to a mystery substance that has left him fighting for his life.Read the full story ›
A man and a worman are critically ill in hospital in Salisbury tonight after it's thought they came in contact with an unknown substance.Read the full story ›
A man & woman have been taken to hospital after coming into contact with an unknown substance in Salisbury. They're in a critical conditionRead the full story ›
A prisoner who went on the run from Salisbury District Hospital has been charged with several offences.
Michal Kisiel gave guards the slip at Salisbury District Hospital on Tuesday while being treated for a head wound.
The 30-year-old was arrested the following evening after being spotted walking past a day nursery in nearby Nunton Village.
He has now been charged with escaping lawful custody, common assault, and threatening an individual with a bladed article.
Kisiel, formerly of Luton, is originally from Poland. has been remanded in custody.