British security services said the men travelled to the UK under the names Alexander Petrov and Ruslan Boshirov, but believe they are aliases and are appealing for help uncovering their true identities.
The suspects fled back to Moscow hours after putting novichok on Mr Skripal’s front door on 4 March, possibly using the same “perfume bottle” that poisonedDawn SturgessandCharlie Rowleyin June.
Police said the men were both using legitimate passports issued by the Russian government and have “travelled extensively” to the UK and other nations in the past, but could not confirm whether they had links to the Kremlin or Russian intelligence agencies.
Investigators have not been able to rule out the existence of other items containing novichok in Britain, and are appealing for guests who stayed in the same London hotel as the alleged assassins to come forward after traces of the nerve agent were discovered in their room.
Assistant Commissioner Neil Basu, the head of UK counterterror policing, said he supported Theresa May’s statement that there was “no alternative conclusion other than that the Russian state was culpable”.
“Clearly this was assassination attempt carried out by people involved in this tradecraft,” he told journalists.
“This was a highly sophisticated attack…the working hypothesis is that theybrought thenovichokinto the country in the box and bottle seen (in released images).”
The Kremlin repeated denials of any involvement in the Salisbury or Amesbury poisonings following Wednesday’s announcement, which a foreign ministry spokesperson claimed the suspects’ names and photos “say nothing to us”.
Maria Zakharova has criticised the UK for turning down Moscow’s request to see case files and Mr Basu confirmed counterterror police had not worked with the Russian state “at any point” or responded to their requests.
The Crown Prosecution Service (CPS) is not applying to Russia for an extradition warrant because the country’s constitution does not permit the extradition of its own nationals.
Instead, European Arrest Warrants and Interpol red notices have been issued, meaning the suspects can be arrested if they leave Russia.
Sue Hemming, director of legal services at the CPS, said the men had been charged with conspiracy to murder Mr Skripal and the attempted murder of the former Russian double agent, his daughter and police officer Nick Bailey, who fell ill after visiting the house.
The men have also been charged with use and possession of novichok contrary to the Chemical Weapons Act and causing grievous bodily harm with intent to Ms Skripal and Mr Bailey.
“Prosecutors have concluded that there is sufficient evidence to provide a realistic prospect of conviction,” Ms Hemming said.
But Mr Basu conceded that the “brutal truth” was that if the suspects do not enter an allied country and get caught, the UK will be powerless to being the suspects to trial, mirroring thwarted efforts to prosecute those responsible for assassinating Russian dissidentAlexander Litvinenko.
“This is not the end of our inquiry,” he added. “Loyalties change, people change and we won’t stop until we get justice.”
Mr Basu said the bottle was a counterfeit Nina Ricci Premier Jour perfume that had been “specially adapted” to contain novichok and distribute it through a pump, adding: “We don’t yet know where the suspects disposed of the novichok they used to attack the door, where Dawn and Charlie got the bottle that poisoned them, or if it is the same bottle used in both poisonings.”