Experts from the United Kingdom defense science and technology laboratory at Porton Down have been unable to identify the origins of the substance Sergei and Yulia Skripal were exposed to. Officials determined that the same substance, found in a perfume bottle in a park weeks later, sickened a man and his girlfriend, who later died.
Mr Fleming, the director of the government's cyber intelligence agency, said GCHQ had supported police in a "painstaking" and "highly complex" investigation into what happened after the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in Salisbury, Wiltshire on 4 March.
The novichok attack left a trail of the deadly nerve agent around Salisbury, with mother-of-three Ms Sturgess dying after she came into contact with the chemical.
The offences include conspiracy to murder Sergei Skripal; the attempted murder of Sergei Skripal, Yulia Skripal and Nick Bailey; the use and possession of Novichok contrary to the Chemical Weapons Act; and causing grievous bodily harm with intent to Yulia Skripal and Nick Bailey.
"Based on the body of intelligence, the government has concluded that the two individuals named by the police and the CPS [Crown Prosecution Service] are officers from the Russian military intelligence service also known as the GRU", British Prime Minister Theresa May told parliament.
"What we have learned today is the specific threat from GRU", May said.
Thursday's statement also noted that an analysis by Britain revealed that the same nerve agent, Novichok, was used in the later poisoning of British citizens Dawn Sturgess and Charles Rowley in June.
"We will not be applying to Russia for the extradition of these men as the Russian constitution does not permit extradition of its own nationals", CPS said in a statement.
Prosecutors deem it futile to apply to Russian Federation for the extradition of the two men, but a European Arrest Warrant has been obtained and the authorities are also seeking the assistance of Interpol.
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Each views the other as a useful partner in checking China's ambitions in Asia and as an ally in counterterrorism efforts. India is planning to buy five S-400 Triumf missile air defence systems from Russian Federation for around $4.5 billion.
Over the course of two days, the men traveled from London to Salisbury, England, twice - once to perform reconnaissance around the Skripals' home, and again to put lethal poison on their front door, police say.
Thus, to obtain the information Zakharova says the British authorities are refusing to share, all Russian authorities need to do is check the passenger manifest for Aeroflot flight SU2588 on March 2, 2018. "We would like to hear from anyone who knows them".
The new info includes the aliases of the two Russian agents: Alexander Petrov and Ruslan Boshirov, now charged with murder (though Moscow will never extradite them).
She said: "Rather than accept responsibility for its actions, the Russian government has offered only denials and counter-accusations".
Basu said traces of Novichok contamination were found in the London hotel room where the two men had stayed.
But Mr Fleming said: "The threat from Russian Federation is real".
Britain, France, Germany, Canada and the United States pledged on Thursday to work to disrupt "the hostile activities of foreign intelligence networks" and called on Russian Federation to disclose its nerve agent program.
Further sanctions, especially if Britain won support from allies in the United States and Europe, could effectively deepen Russia's economic isolation.