Theresa May told parliament that the pair of Russian suspects who have been charged with carrying out the Salisbury nerve agent attack were members of the GRU, Russia's military intelligence service.
Speaking after the Crown Prosecution Service announced they had enough evidence to charge Alexander Petrov and Ruslan Boshirov over the March poisoning, the prime minister told MPs: "The GRU is a highly-disciplined organisation with a well-established chain of command. So this was not a rogue operation.
"It was almost certainly also approved outside the GRU at a senior level of the Russian state."
Investigators believe it is likely the pair travelled under aliases and that Petrov and Boshirov are not their real names.
Then they are accused of putting the novichok nerve agent on the front door of former Russian spy Sergei Skripal's Salisbury home. He was poisoned along with his daughter Yulia on 4 March.
Police said CCTV shows the two suspects in the vicinity of the property on that date. Hours later, the men left the UK on a flight from Heathrow to Moscow.
As Russia does not extradite its citizens, investigators have not applied to do so. Instead a European Arrest Warrant has been issued, which would allow them to be detained if they leave their homeland.
