"This was not a rogue operation", May told Parliament.
"It was nearly certainly also approved outside the GRU at a senior level of the Russian state". The final images show the men leaving from London Heathrow Airport in the evening of March 4.
Mr Skripal and his daughter Yulia were found unconscious on a bench outside a shopping centre in Salisbury on 4 March.
She stopped short of blaming Russian President Vladimir Putin but said the attack was likely created to "give a message to those Russians who were living elsewhere who had been involved in matters relating to the Russian state".
Police officers guard a cordon around a police tent covering the the spot where former Russian double agent Sergei Skripal and his daughter were found critically ill following exposure to an "unknown substance" in Salisbury, England, March 7, 2018. They said the men flew from Moscow to London on Russian passports.
Russia's Foreign Ministry said Thursday, after the charges were announced, that the two names given by the British authorities, "do not mean anything to us", according to Russian state-run news agency RIA.
"The levels of Novichok we found in the room at the time of police sampling in May were such that they were not enough to cause short or long-term health effects to anyone exposed to it, at that point or thereafter", he said.
He confirmed that the police were in "no doubt" that the attack on the Skripals in March had been linked with events in nearby Amesbury, which poisoned Dawn Sturgess and Charlie Rowley in July and led to the death of 44-year-old Sturgess.
Wiltshire local woman Dawn Sturgess died after inadvertently spraying herself with the Novichok virus which was inside a discarded perfume bottle.
The men will also be charged with possession of novichok, a deadly Soviet-era poison that's banned by the Chemical Weapons Act. It had been held in a pink box, falsely labeled as Nina Ricci Premier Jour perfume. Police said Novichok was applied to the front door of the Skripal's home.
Hemming said the United Kingdom is not asking Moscow to extradite the suspects because Russian law forbids extradition of its citizens. Russian Federation reiterates that it has no connection to either the Salisbury or Amesbury attacks, adding that co-operation with Britain remains vital. The current charges relate to his and the Skripals' case.
Mr Basu said the two suspects returned to Russian Federation on 4 March. Britain won't even ask for their extradition to stand trial on charges of attempted murder because prosecutors believe it would be futile. He warned, however, that "it is likely that they were travelling under aliases and that these are not their real names".
Russia's envoy to the Organization for the Prohibition of Chemical Weapons (OPCW) said Moscow had nothing to do with the poisoning, RIA news agency reported.
Assistant police commissioner Neil Basu would not say whether investigators believe the suspects worked for Russian security services but, he added: "This was a sophisticated attack across borders". They also provided the first images of the sample-size perfume bottle that was used to apply the poison to the front door of Russian ex-spy's home in the city.
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Tehran has provided steady political, financial, and military support to the government during this period. He could not specify their nationalities or whether they belonged to militias or government forces.