The global chemical weapons watchdog has said that former Russian spy Sergei Skripal and his daughter Yulia were poisoned by the Novichok nerve agent, confirming the UK government's position that a Russian-made substance was used in the attempted murder of the pair in Salisbury on 4 March.
The Organisation for the Prohibition of Chemical Weapons stopped short of naming the nerve agent as Novichok in a statement released on Thursday, but said it agreed with the UK's findings, which were based on scientific tests at Porton Down, the weapons research centre.
Novichok is thought to have been developed in the Soviet Union between the 1970s and the 1990s, although Russia has denied that weapons research was carried out under this name.
Sergei Skripal remains in hospital in serious condition, while Yulia Skripal has been released. A police officer, detective sergeant Nick Bailey, was inadvertently poisoned after tending to the Skripals, but was released from hospital on 22 March.
Russia has continually denied any involvement in the incident, but the UK is adamant that there is no alternative explanation other than that the attack was ordered by the Russian state.
Boris Johnson, the foreign secretary, said in a statement: "Today the international chemical weapons watchdog have confirmed the findings of the United Kingdom relating to the identity of the toxic chemical used in the attempted assassination of Mr Skripal and his daughter, and which also resulted in the hospitalisation of a British police officer. That was a military grade nerve agent – a Novichok.
"This is based on testing in four independent, highly reputable laboratories around the world. All returned the same conclusive results.
"There can be no doubt what was used and there remains no alternative explanation about who was responsible – only Russia has the means, motive and record."
Johnson added that the decision was taken to publish the full OPCW executive summary because "unlike the Russians, we have nothing to hide".
"We will now work tirelessly with our partners to help stamp out the grotesque use of weapons of this kind and we have called a session of the OPCW Executive Council next Wednesday to discuss next steps. The Kremlin must give answers," he said.
The OPCW's investigators came to the UK on 19 March and took medical information, blood samples, and samples from different parts of Salisbury.
According to a statement from the OPCW, "The results of analysis by the OPCW designated laboratories of environmental and biomedical samples collected by the OPCW team confirm the findings of the United Kingdom relating to the identity of the toxic chemical that was used in Salisbury and severely injured three people."
The statement noted that the chemical used was of "high purity". A fuller report is being released to the British and Russian governments.
Breaking: chemical weapons watchdog confirms UK correctly identified substance used to poison Skripals (ie it was novichok). Of "high purity”. Toxic chemical’s name, structure given in classified report. https://t.co/JS8dM8Z8bn https://t.co/T7NAhIIEgU
On Wednesday night, Yulia Skripal released a statement to say she had rejected help from the Russian Embassy in London.
Yulia Skripal, 33, made the comments in a statement released through the Metropolitan Police on Wednesday, two days after she was discharged from hospital.
"I have access to friends and family, and I have been made aware of my specific contacts at the Russian Embassy who have kindly offered me their assistance in any way they can. At the moment I do not wish to avail myself of their services, but, if I change my mind I know how to contact them," she said.
She added that her father remains "seriously ill", and that she is suffering from the attack. She is in the care of "trained officers" who are taking her through the investigative process.
"I find myself in a totally different life than the ordinary one I left just over a month ago, and I am seeking to come to terms with my prospects, whilst also recovering from this attack on me," she said.
"Most importantly, I am safe and feeling better as time goes by, but I am not yet strong enough to give a full interview to the media, as I one day hope to do. Until that time, I want to stress that no one speaks for me, or for my father, but ourselves."
The Skripals' poisoning provoked a diplomatic crisis between Russia and the UK, as well as other Western governments, resulting in the expulsion of more than 150 diplomats on each side.
The Russian Embassy in London cast doubt on the authenticity of Yulia Skripal's statement, saying it indicates the UK's "forcible isolation of the Russian citizen".
"If everything mentioned there is true we cannot but congratulate our compatriot. However, with no possibility to verify it, the publication by the Metropolitan Police raises new questions rather than gives answers," it said.
"As before, we would like to make sure that the statement really belongs to Yulia. So far, we doubt it much. The text has been composed in a special way so as to support official statements made by British authorities and at the same time to exclude every possibility of Yulia’s contacts with the outer world – consuls, journalists and even relatives."
It expressed surprise that she had access to friends and family.
"Not a single friend or relative quoted by Russian or British media confirms such contacts," it said, noting that "as far we know" their closest relatives are her cousin Victoria and their grandmother, Elena, who live together.
"A question arises: what family is Yulia in contact with?"
Last week Russian state TV played what it claimed was a recording of a phone conversation between Yulia and her cousin, in which Yulia is quoted as saying "everyone is recovering and alive".
"We have also noticed the apparent contradiction between the phone conversation in which Yulia says to Victoria that 'everything is fine' with her and her father, and their health condition as described in today’s Met Police statement," the embassy added.