"We are now reviewing the Russian Government's note informing us of their response".
"Remember, this is the first time that a weapons-grade nerve agent, Novichok, has been used outside of war on allied soil".
"Of course, we expected such a step from Russian Federation and it doesn't come as a surprise".
The Russian Foreign Ministry said in a statement on Friday it was summoning the representatives of a "raft of countries" that had taken what it called unfriendly action against Russia in solidarity with Britain because of the Skripal affair.
Many other countries have expelled one or two diplomats, a move created to register support for the UK.
The moves came in retaliation for the coordinated expulsion of Russian diplomats by Britain and its allies over a nerve agent attack against former double agent Sergei Skripal and his daughter Yulia in the English city of Salisbury on March 4. British authorities on Thursday said Yulia was showing signs of recovery, while her father remained in serious but stable condition.
Last week, the United Kingdom had suspended 21 Russian diplomats back to Moscow, claiming that Russia was "highly responsible" for the poisoning attack.
The Russian Foreign Ministry said Bristow had been told London had just one month to cut its diplomatic contingent in Russia to the same size as the Russian mission in Britain.More news: Single Mega Millions ticket sold in New Jersey wins $521 million jackpot
More news: Brathwaite, Holder opt out of Windies T20 series in Pakistan
More news: Angels-Dodgers spring finale comes to an early, and very smelly, ending
Preparations appeared to be under way on Friday to close the St Petersburg mission down, with a removals truck making repeated journeys to and from the consulate which took delivery of a large pizza order for its staff. It also warned USA authorities against seizing any Russian state assets in America, saying that would lead "to the further serious degradation in our relations, with extremely grave consequences for global stability".
Russians watching the activity expressed mixed views on the consulate's closure.
"We invite the United States authorities who are encouraging a slanderous campaign against our country to come back to their senses and stop thoughtless actions to destroy bilateral relations", it said.
Russia is expelling two Italian diplomats as a tit-for-tat response to Rome's expulsion of Russian diplomats, ARMENPRESS reports, citing TASS, the Italian Foreign Ministry said in a statement on Friday.
Adding to the tensions, the ministry late Friday said a plane belonging to Russian state airline Aeroflot was being searched by police in London.
Foreign Ministry Spokeswoman Maria Zakharova said that meant Britain would have to cut "a little over 50" additional diplomats in Russian Federation.
Lavrov vowed at the briefing in Moscow that "we want to establish the truth" over the poisoning and accused Britain of "making a mockery of global law".
Mr Lavrov said that Moscow called a meeting on Monday of the secretariat of the Organisation for the Prohibition of Chemical Weapons to discuss the case.