On Saturday, the Russian foreign ministry tweeted an RT interview with Alexander Shulgin, Russia's permanent representative to the Organisation for the Prohibition of Chemical Weapons (OPCW), in which he suggested British authorities were "afraid". "Twenty three diplomatic staff at the British embassy in Moscow are declared persona non grata and to be expelled within a week", said a statement.
Escalating a crisis in relations, Russian Federation said it was also shutting down the activities of the British Council, which fosters cultural links between the two countries, and withdrawing agreement for Britain to operate a consulate-general in St. Petersburg.
Russian Foreign Ministry spokeswoman Maria Zakharova said on Friday Moscow had already decided on retaliatory measures, which she said Britain would be informed of in the near future.
The ministry said it had also warned Britain that "if further unfriendly actions are taken towards Russia, the Russian side retains the right to take other answering measures".
On Wednesday British Prime Minister Theresa May announced a series of measures against Russia over its failure to respond to the British government's request to explain how a military-grade nerve agent was used in a recent attack on former Russian spy Sergei Skripal and his daughter.
It said this was a response to Britain's "provocative actions" and "baseless accusations over the incident in Salisbury on March 4".
Sergei Skripal was sentenced to 13 years in prison in 2006 for spying for Britain, according to Russian state media accounts of the closed hearing.
The response from Moscow is robust and does go further than the United Kingdom measures.
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Counter-terrorism police have also renewed their appeal for sightings of Mr Skripal's burgundy BMW 320D saloon vehicle, registration HD09 WAO, in Salisbury on the morning of March 4.
"The attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian state was culpable".
Bristow told reporters: "We will always do what is necessary to defend ourselves, our allies and our values against an attack of this sort, which is an attack not only on the United Kingdom, but upon the worldwide rules-based system on which all countries, including Russian Federation, depend for their safety and security", according to The Associated Press. The British Council is a cultural institute with artistic, language and educational programs. United Kingdom officials believe the Skripals were exposed to a nerve agent known as Novichok that was developed in Russian Federation. They remain in critical condition in hospital. The UK also said it would crack down on Russian oligarchs who stash money in London real estate and banks. There's no evidence at this stage that his death and the attack on the Skripals are linked, it said.
On Friday, police said they were treating the March 12 death of exiled businessman Nikolai Glushkov as murder after a post-mortem found he died from "compression to the neck".
A Russian lawmaker is warning Britain against escalating the crisis over the poisoning of a former Russian spy.
A Russian lawmaker is blaming Britain for the escalating tensions between London and Moscow over the nerve agent poisoning of a former Russian double agent and his daughter.
CNN's Matthew Chance reported from Moscow and Laura Smith-Spark wrote and reported from London.