In a joint statement reiterating their "outrage", the leaders said they were completely confident the attempted killing of former Russian double agent Sergei Skripal on British soil in March "was nearly certainly approved at a senior government level" in Russia.
The poisoning was "not a rogue operation" and was "almost certainly" approved at a senior level of the Russian state, she said.
Britain produced an "unfounded and mendacious cocktail of facts" and is refusing to cooperate with Russia in investigating the poisoning "to unleash a disgusting anti-Russian hysteria and to involve other countries in this hysteria", Nebenzia said.
A spokeswoman for the Russian foreign ministry said Wednesday it had no knowledge of Petrov or Boshirov, and accused British authorities of manipulating information in the case.
Sue Hemming of the Crown Prosecution Service said the United Kingdom wouldn't ask Moscow to extradite the men because Russian law forbids extradition of the country's citizens.
"We now have sufficient evidence to bring charges in relation to the attack on Sergei and Yulia Skripal in Salisbury and domestic and European arrest warrants have been issued for the two suspects".
"We got a swift response in March and we have done so again and we are thankful for that support", he said. He moved to England in 2010 as part of a spy swap.
Sergei Skripal, the former Russian spy, and his daughter collapsed in downtown Salisbury after being exposed to the poison on Skripal's front door on March 4, police said.
Skripal's daughter Yulia and a police officer who attended the scene also fell ill in the case, which has caused the biggest East-West diplomatic expulsions since the Cold War.
Russian Federation has repeatedly denied any involvement in the attack, which also sickened a British police officer and been linked to the death of a British woman, Dawn Sturgess, who accidentally came in June came contact with the same substance, which was developed by the Soviet Union as a chemical weapon.
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Police on Wednesday gave new details about what Basu called "one of the most complex investigations" the force had ever seen. British police believe the names are aliases, although the two men travelled on authentic Russian passports.
Her partner Charlie Rowley had found a perfume bottle, falsely labelled as "Premier Jour" by Nina Ricci, which police said contained a "significant amount of Novichok". He was hospitalized and his girlfriend Dawn Sturgess died after being exposed to the contents.
Police are still trying to determine where the bottle was between the Skripal poisoning in March and its discovery by Rowley on June 27.
Sergei Skripal and his daughter Yulia survived nerve-agent poisoning in Britain after spending weeks in hospital. Sturgess later died from exposure to the agent.
A British inquiry in 2016 concluded that Russian President Vladimir Putin probably approved Litvinenko's murder, an accusation that Moscow has always rejected.
Russian defense and security analyst Pavel Felgenhauer said authorisation to attack the Skripals had also likely come "from the very top".
Media captionWhat do we know about the Russian intelligence organisation, the GRU?
Moscow strongly denies involvement in the attack, and Russian officials said they didn't recognize the suspects.
May said Britain and its allies would "step up our collective efforts" against the agency, though she did not name any specific measures.