Russia will expel 23 British diplomats and close the British Consulate in St. Petersburg as part of its response to London’s decision to expel Russian diplomats in an escalating row over the poisoning of a former spy and his daughter in Britain earlier this month.

The Russian Foreign Ministry said Saturday that “23 diplomatic personnel from the British Embassy in Moscow have been declared persona non grata” and have one week to leave. The closure of the consulate in St. Petersburg was not given a firm deadline, with the Foreign Ministry saying only that consulate employees will be given sufficient time to finish their work.

The move comes a day before Russia’s presidential election, which President Vladi­mir Putin is expected to win.

Britain on Wednesday ordered the expulsion of 23 Russian diplomats, many of whom were said by Prime Minister Theresa May to be Russian intelligence officers, after Moscow ignored an ultimatum to provide an explanation for how a Russian nerve agent came to be used in the poisoning of a former spy on British soil.

The spy, 66-year-old Russian double agent Sergei Skripal, and his 33-year-old daughter, Yulia, were found slumped on a park bench in Salisbury on March 4. After several days of investigation, British authorities determined that they were poisoned with a nerve agent known as Novichok, believed to be unique to Russia.

The Skripals are reported to be in critical condition, but British authorities have provided no further information about their status. Russia has demanded consular access to Yulia Skripal, a Russian citizen, and complained that Britain has not responded to that request. Russia’s Investigative Committee opened a criminal case Friday into Yulia Skripal’s attempted murder.

The British government said it was expecting the retaliatory expulsions from Russia.

Speaking at her party’s spring forum in London, May said Britain would “consider our next steps in the coming days, alongside our allies and partners.”

“We will never tolerate a threat to the life of British citizens and others on British soil from the Russian government,” she said, prompting applause.

The British Foreign Office offered its own harsh words.

“Russia’s response doesn’t change the facts of the matter — the attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian State was culpable. It is Russia that is in flagrant breach of international law and the Chemical Weapons Convention,” the Foreign Office said in a statement.

Russia was slow to respond to May’s decision, spending Thursday and Friday promising a swift and strong response. When Moscow finally made its announcement Saturday, it went slightly beyond strictly reciprocal measures.

The Foreign Ministry said it would also order an end to all activities in the country of the British Council, Britain’s international organization for cultural relations and educational opportunities, and warned London that “if any further unfriendly actions are taken against Russia, the Russian side reserves the right to take other retaliatory measures.”

This is not the first time the British Council, an organization that promotes cultural exchange, has been caught up in retaliations. In 2008, the British Council’s regional offices in St. Petersburg and Yekaterinburg were closed, leaving only the head office in Moscow open.

The closure of the offices, ordered by Russia’s Foreign Ministry, followed the expulsion of Russian diplomats in Britain over the 2006 poisoning of ex-KGB operative Alexander Litvinenko in London.

Stephen Kinnock, a British lawmaker who was the director of the British Council in St. Petersburg before it closed, told the BBC that the latest move shows “how mean-spirited and vindictive the Putin regime really is.”

Vladimir Dzhabarov, first deputy of the foreign affairs committee in Russia’s upper house of parliament, told Moscow-based Interfax news agency that the British Council was used as a cover organization for British intelligence officers. It has been a target for Russian authorities since most of its operations were closed by authorities in many Russian regions 10 years ago. It retained an office in Moscow.

“Those measures should sober British politicians up,” Dzhabarov said, “primarily Foreign Secretary Boris Johnson, who dared to make an offensive statement regarding the head of a great state, virtually accusing him of ordering the poisoning of Skripal.”

Johnson on Friday had said it was “overwhelmingly likely” that it was Putin’s decision “to direct the use of a nerve agent on the streets of the U.K.”

Alexei Chepa, deputy head of the foreign affairs committee in Russia’s lower house of parliament, said Saturday that he expected additional measures to be taken by the British government in response to Russia’s actions today. “Now we are warning the [British] that we will respond in an adequate manner to all further steps of this nature.”

Britain had been widely expecting a robust response from Russia, but it was immediately unclear whether there would be further retaliatory moves.

When asked what Britain should do next, Tom Tugendhat, a Conservative lawmaker and chair of the foreign affairs select committee, told the BBC: “I think what we got to do is focus entirely on the Putin regime, the Putin family and the Putin henchmen, and focus on their money, much of which is hidden in Western Europe.”

Others warned against a drawn-out standoff.

Roderic Lyne, Britain’s former ambassador to Russia, told the BBC: “I don’t think it would be sensible to get dragged down into a mud-wrestling battle with a gorilla.”

Adam reported from London.