The Russian Foreign Ministry summoned the British ambassador, Laurie Bristow, to a meeting on Saturday morning in central Moscow at its headquarters during which he was informed of the retaliatory measures.
Russian Federation is to expel 23 British diplomats amid tensions over the nerve agent attack on a former spy and his daughter in the UK.
The ministry said Moscow's measures were a response to what it called Britain's "provocative actions and groundless accusations". She said Britain is taking a tough line because of frustration at recent advances of Russian-backed Syrian government forces against Western-backed rebels. It has cast Britain as a post-colonial power unsettled by its impending exit from the European Union, and even suggested London fabricated the attack to whip up anti-Russian hysteria.
The Russian foreign ministry said staff from the UK's Moscow embassy would be expelled within a week.
"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 global rules-based system on which all countries, including Russian Federation, depend for their safety and security", Bristow told reporters. "We can be reassured by the strong support we have received from our friends and allies around the world", May said at the Conservative Party's spring forum in London. It had warned London it stood ready to take further measures in the event of more "unfriendly steps". United Kingdom officials believe that the Skripals were exposed to nerve agent known as Novichok, which was developed in Russian Federation.
Britain's foreign secretary accused Russian President Vladimir Putin of personally ordering the poisoning of the Skripals.
"The origins of the nerve gas appear to be Russian, therefore the challenge has to be to the Russian government but also we and the Russian government are both signed up to an global Chemical Weapons Convention".
In comments to reporters after he left the Foreign Ministry, Bristow said the crisis had arisen because of "the attempted murder of two people using a chemical weapon developed in Russian Federation and not declared by Russian Federation".
Radical Brazilian Politician Marielle Franco Assassinated
Amnesty International said the probe should be rigorous and focus on "the context, motive and responsibility" for the killing. Franco was shot several times as bullets sprayed her vehicle as it drove through Rio de Janeiro's unsafe north side.
Skripal, a former Russian intelligence officer, and his 33-year-old daughter Yulia were found unconscious on a bench at a shopping center in the district of Salisbury, Britain, on March 5, and are still in critical condition, according to reports.
"We anticipated a response of this kind and the National Security Council will meet early next week to consider next steps", said Britain's Foreign Office.
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.
Military personnel wearing protective suits remove a police auto and other vehicles from a public auto park on March 11, 2018, in Salisbury, England.
About 400 witnesses have already come forward in what is "extremely challenging and complex investigation", Assistant Commissioner Neil Basu of London's Metropolitan Police said.
A United Kingdom inquiry found that two Russian agents poisoned Litvinenko at a London hotel bar in 2006 by spiking his tea with highly radioactive polonium-210, and that Putin "probably approved" Litvinenko's killing.