Russia has accused the U.K. of going “completely insane” after British Prime Minister Theresa May pledged to kick out 23 Russian diplomats in retaliation for the attempted murder of its former spy on British soil. Foreign Minister Sergei Lavrov vowed that British diplomats in Russia would be thrown out “soon” as tensions sharply escalated between Russia and the West after the nerve-agent attack on Sergei Skripal. Russia’s outburst came a day after the U.S. gave its unequivocal backing to Britain’s position, with the White House saying it “stands in solidarity” with “its closest ally.” Speaking Thursday morning, Russian Foreign Ministry spokeswoman Maria Zakharova condemned “the statements made by the prime minister of Britain in parliament with completely insane accusations toward the Russian Federation, our entire country, our entire people.” Lavrov, asked if Russia would kick out British diplomats, said: “Absolutely. Soon. I promise you that.” Meanwhile, Russia has accused the U.K. of conspiring to block a Russian statement about the attempted murders at the United Nations Security Council, which called for an international investigation into the attack.