The location of a secret lab where a nerve agent was created that was used to allegedly poison a former Russian spy and his daughter has been revealed for the first time.
According to The Times in London, a Russian military research base was where the original nerve agent came from that was used in the shocking attack on Sergei Skripal and his daughter Yulia in Salisbury.
Britain blames Russia for the poisoning on UK soil of the former double agent and his daughter with what it says was a Soviet-made military-grade nerve agent, a charge the Kremlin furiously denies.
But The Times reports that a British intelligence briefing for its allies has confirmed the novichok chemical was manufactured at the Shikhany facility in southwest Russia.
The high-level briefing was reportedly used to convince world leaders that Moscow was behind the attack which has sparked an international crisis.
The ongoing investigation has sent relations between Russia and the West plummeting with the biggest wave of tit-for-tat expulsions of diplomats in recent memory.
More than 150 Russian diplomats from 28 countries have been expelled. Russia has also retaliated by expelling Western diplomats.
The intelligence briefing also reportedly suggested that Shikhany was used during the past decade to test whether the weapons-grade novichok nerve agent could be effective for assassinations abroad.
Stockpiles found at Shikhany were far smaller and may have been used in targeted killings, the Times reports.
Hamish de Bretton Gordon, the former commander of Britain's Chemical, Biological, Radiological and Nuclear Regiment, who has seen the intelligence, said: "The intelligence Britain has clearly points to Russia and Shikhany. No doubt the Russians are scrubbing it down as we speak."
Mr de Bretton Gordon said that there was nothing to support claims the nerve agent may have been sourced from another neighbouring country like the Ukraine or Uzbekistan.
The news of the military base location comes as Yulia said she is recovering, in her first public statement since the attack, as Moscow and London unleashed a new war of words during a bitter session at the UN Security Council.
In the latest expulsions, some 60 US diplomats who were ordered to leave flew out of Moscow airport early Thursday.
A few hours later British authorities released a statement from Yulia commenting on her recovery.
"I woke up over a week ago now and am glad to say my strength is growing daily," she was quoted as saying in comments released by the police.
That statement came on a day of furious rhetoric between Moscow and London at the UN Security Council.
Russia unleashed a blistering war of words against Britain deflecting accusations of poisoning a former double agent in England with Moscow's envoy issuing a series of denials and colourful insults.
"It's some sort of theatre of the absurd. Couldn't you come up with a better fake story?" Vastly Nebenzia, told the council. "We have told our British colleagues that 'you're playing with fire and you'll be sorry.'" British Ambassador Karen Pierce was on similarly fiery form. "I won't take any lectures on morality or on our responsibilities," said Pierce, "from a country that, as this council debated yesterday, has done so much to block the proper investigation of the use of chemical weapons in Syria."
At one point in the clash Nebenzia mused on the whereabouts of reported Skripal pets, two cats and two guinea pigs.
"What happened to these animals? Why doesn't anyone mention them? Their condition is also an important piece of evidence," he said.
A British government spokeswoman later told AFP that both guinea pigs had died and that a cat found in a distressed state was euthanized. She did not mention a second cat.
Yulia and her father Sergei, a former double agent, were found in a critical condition on a public bench in the English city of Salisbury last month.
Yulia appears to have made more of a recovery than her father, who remains unconscious.
Russian state television earlier aired an unverified recording of a phone conversation between Yulia and her cousin who lives in Moscow.
In the call, a woman introducing herself as Yulia Skripal said she was expecting to be discharged from hospital soon and that her father Sergei was "fine".
The hospital where the pair are being treated said in their latest update last week that Sergei remained in a critical condition.
Russia called for UN Security Council talks a day after it failed to win diplomatic support for a joint probe of the spy poisoning at a meeting of the global chemical watchdog, the Organisation for the Prohibition of Chemical Weapons (OPCW).
The OCPW meeting also saw a day of bitter rhetoric between Moscow and Britain and its western allies.
London slammed the joint probe idea as "perverse".
British Foreign Secretary Boris Johnson hailed the defeat of Russia's bid. "The purpose of Russia's ludicrous proposal at The Hague was clear — to undermine the independent, impartial work of the international chemical weapons watchdog," he said, adding that Moscow's main goal was "to obscure the truth and confuse the public." Britain is carrying out its own probe, with independent technical assistance from OPCW experts.
Sergei Naryshkin, head of Russia's SVR foreign intelligence, warned that both sides must avoid tensions escalating to the dangerous levels of the Cold War.
He called the affair a "grotesque provocation... crudely concocted by the British and American security services." OPCW experts have already taken on-site samples which are being analysed in The Hague, as well as in four other certified laboratories. The watchdog said it expected the results by early next week.
But in a move hailed as a vindication by Moscow, the British defence laboratory analysing the nerve agent revealed Tuesday that it could not say whether the substance came from Russia.
The Kremlin immediately demanded an apology from Prime Minister Theresa May and her government for implicating Putin in the nerve agent attack, saying this "idiocy has gone too far." On Thursday, The Times newspaper cited British security sources saying they believe they have pinpointed the location of a Russian laboratory where the nerve agent used in Salisbury was manufactured.
The conflict has entered its seventh day.