By Adewale Samson with Agency Reports

Britain will expel two dozen Russian diplomats, severe high-level bilateral contacts with Moscow and take both open and covert action against Kremlin meddling after the poisoning of a former spy, plunging U.K.-Russian relations into their deepest freeze since the Cold War.

Prime Minister Theresa May has made known that 23 Russian diplomats who have been identified as undeclared intelligence officers have a week to leave the country, reports BBC.

May spoke after Moscow ignored a midnight deadline to explain how a nerve agent developed by the Soviet Union was used against Sergei Skripal, an ex-Russian agent convicted of spying for Britain, and his daughter Yulia. They remain in critical condition in a hospital in Salisbury, southwestern England, after being found unconscious on March 4.

Russia had provided no explanation, and “there is no alternative conclusion other than that the Russian state was culpable for the attempted murder of Mr. Skripal and his daughter.”

A range of economic and diplomatic measures, including the suspension of high-level contacts with Russia. An invitation for Russian Foreign Minister Sergey Lavrov to visit Britain has been cancelled, and May said British ministers and royals won’t attend the soccer World Cup in Russia this summer.

Britain would clamp down on murky Russian money and strengthen its powers to impose sanctions on abusers of human rights.

The Russian Embassy in London said the expulsion of diplomats was “totally unacceptable, unjustified and shortsighted.”

“All the responsibility for the deterioration of the Russia-U.K. relationship lies with the current political leadership of Britain,” it said in a statement.

Russian Ambassador Alexander Yakovenko said Britain’s actions were “a provocation.”

Some Russia experts said the measures announced by May were unlikely to make Russian President Vladimir Putin’s government change its behaviour. She didn’t expel Russia’s ambassador or announce sanctions against any individuals.

Critics of the British government have long claimed that the U.K. is reluctant to act against Russia because London’s property market and financial sector are magnets for billions in Russian money.