The international chemical weapons watchdog on Thursday confirmed Britain's finding that a former Russian spy and his daughter were poisoned with a nerve agent, as Russia continued to deny suggestions that it was behind the attack.
Investigators from the Organization for the Prohibition of Chemical Weapons, a Nobel Peace Prize-winning group, said the nerve agent was "of high purity." Britain says that means only a state with a sophisticated laboratory could have manufactured it.
The watchdog's report does not say who was responsible for the attack, since that was outside the scope of its mission. The OPCW's job was to identify the poison, not to trace its origins or assign blame.
Britain blames Russia for the March 4 poisoning of Sergei Skripal and his daughter Yulia in the English city of Salisbury. Russia denies involvement, saying Britain hasn't provided any evidence for its assertion. Britain has called for an OPCW meeting next week to discuss the results of the organization's report.
In a published summary of its findings, the OPCW did not name Novichok, the type of nerve agent previously cited by British Prime Minister Theresa May. But it confirmed "the findings of the United Kingdom relating to the identity of the toxic chemical that was used in Salisbury." It said the name and structure of the toxin were included in the full classified report, distributed to 192 member states of the organization.
The Novichok class of nerve agents was developed in the Soviet Union toward the end of the Cold War, and Britain says it has evidence Russia has continued to manufacture Novichok agents in the last decade. Russia denies this and says the nerve agent used on the Skripals could easily have been manufactured in another country.
The OPCW report said the nerve agent used on the Skripals was "of high purity." The purity makes it hard to tell when the agent was manufactured, since without impurities it does not degrade over time.
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Britain says scientific analysis of the poison is only one of the factors that has led it to blame Russia.
Others include intelligence that Russia has made nerve agents and studied how to use them for assassinations, and the view of Russian President Vladimir Putin's government that traitors are legitimate targets.
But the U.K. does not possess a scientific smoking gun — a sample of Novichok from a Russian lab to compare with the Salisbury samples.
Georgy Kalamanov, Russia's deputy minister of industry and trade, told the Interfax news agency Thursday it's impossible to pinpoint the agent's origin and reaffirmed Moscow's demand for a probe that would involve Russia.
U.K. Foreign Secretary Boris Johnson welcomed the OPCW's report, saying tests in four independent laboratories around the world all returned the same 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," he said.
The findings come after Yulia Skripal rejected Russian Embassy assistance as she recovers at an undisclosed location. Yulia, 33, was released from the hospital earlier this week, but her 66-year-old father is recovering more slowly.
"I am not yet strong enough to give a full interview to the media, as I one day hope to do," Yulia Skripal said in a statement released Wednesday by London's Metropolitan Police. "Until that time, I want to stress that no one speaks for me, or for my father, but ourselves."
The comment came after Yulia's cousin Viktoria gave a series of interviews about a telephone conversation between the two, leading the British government to claim that Russia was using Viktoria Skripal as a "pawn" in the poisoning dispute.
Russia's Embassy in London questioned the authenticity of Yulia's statement, saying it was crafted to support Britain's version of events and increases suspicions that she is being held against her will.
British authorities "must urgently provide tangible evidence that Yulia is alright and not deprived of her freedom," the Russian embassy said.
"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," the embassy said. "The document only strengthens suspicions that we are dealing with a forcible isolation of the Russian citizen."
The poisoning dispute has led to severe tensions between Russia and the West, and to the expulsions of hundreds of diplomats between them.