MOSCOW — Prime Minister Theresa May said the UK may take further action against Russia over the nerve-agent poisoning of a former spy and his daughter after Moscow ordered 23 British diplomats to leave the country in a tit-for-tat retaliation.

鈥淲e anticipated a response of this kind and we will consider our next steps in the coming days, alongside our allies and partners,鈥 Ms. May said at a Conservative Party forum in London on Saturday. Russia also ordered the British consulate in St. Petersburg to close and told the British Council to end its work in the country.

The Foreign Ministry in Moscow summoned UK Ambassador Laurie Bristow on Saturday to tell him of the retaliation for Ms. May鈥檚 expulsion of 23 Russian diplomats from London. The measures were in response to 鈥渢he provocative actions of the British side and the unsubstantiated accusations鈥 against Russia, the ministry said. The confrontation escalated after Ms. May accused Moscow on Wednesday of an 鈥渦nlawful use of force鈥 involving a weapons-grade nerve agent and ordered out the largest number of Russian diplomats from London in 30 years. She also broke off all high-level contacts over the chemical attack that poisoned former Kremlin double-agent Sergei Skripal and his daughter Yulia in the city of Salisbury on March 4. The pair remain in critical condition.

鈥楢PPALLING ATTACK鈥
The first use of a nerve agent on European soil since World War II is a direct challenge to the Western alliance, days before elections are almost certain to give Vladimir Putin a fourth term as Russia鈥檚 president. Tensions heightened further when UK Foreign Secretary Boris Johnson said Friday that it was 鈥渙verwhelmingly likely鈥 Mr. Putin personally ordered the operation, a comment described as 鈥渦npardonable diplomatic misconduct鈥 by the Kremlin.

Mr. Johnson added to his Putin criticism on Saturday, writing in the Washington Post that the nerve-agent incident is 鈥減art of a pattern of reckless behavior鈥 by the leader, citing Russia鈥檚 annexation of Crimea, cyberattacks in Ukraine, the hacking of Germany鈥檚 parliament and Russia鈥檚 interference in foreign elections.

鈥淭his crisis has arisen as a result of an appalling attack鈥 in the UK involving 鈥渁 chemical weapon developed in Russia and not declared by Russia at the Organisation for the Prohibition of Chemical Weapons, as Russia was and is obliged to do,鈥 Mr. Bristow told reporters in televised comments as he left the ministry.

Russia gave the British diplomats one week to leave. 鈥淚f further actions of an unfriendly nature are taken against Russia, the Russian side reserves the right to take other retaliatory measures,鈥 the ministry said.

BACKING MAY
The UK National Security Council will meet early next week to 鈥渃onsider next steps,鈥 the Foreign and Commonwealth Office in London said in a statement on Saturday. 鈥淲e continue to believe it is not in our national interest to break off all dialogue between our countries but the onus remains on the Russian state to account for their actions.鈥

US President Donald J. Trump, German Chancellor Angela Merkel and French President Emmanuel Macron backed the UK in a joint statement with Ms. May on Thursday and said there鈥檚 鈥渘o plausible alternative explanation鈥 to Russian responsibility.

Russia denies involvement and warned for days that it would reply to the UK鈥檚 expulsion of 40% of its diplomats in London. Foreign Minister Sergei Lavrov has denounced the British accusations as 鈥渁bsolutely rude, unsubstantiated and baseless.鈥

Russia鈥檚 response is 鈥渕oderate, expected and appropriate,鈥 said Oleg Morozov, a former senior Kremlin official who now sits on the foreign affairs committee of the upper house of parliament. 鈥淚t鈥檚 impossible not to respond in this situation. Britain is acting too defiantly.鈥

COUNCIL CLOSING
The order to close the British Council ends nearly 60 years of its work in Russia as the UK鈥檚 international organization for culture and education. It opened offices in Moscow under a 1959 agreement with the Soviet Union and expanded to 15 Russian cities after the 1991 collapse of the Communist state.

Its presence gradually reduced amid mounting political confrontation between the UK and Russia, which also disputed the legal basis for the council鈥檚 presence in the country. In 2008, Russia ordered the council to close all its offices except the Moscow headquarters as part of retaliation for the UK鈥檚 expulsion of diplomats over the radioactive poisoning of former security-service officer Alexander Litvinenko in 2006. A UK public inquiry concluded in 2016 that Putin 鈥減robably鈥 approved the killing.

Russia鈥檚 attacking the wrong target with its 鈥渕isguided鈥 decision to close the council, Clementine Cecil, executive director of the Pushkin House center in London, which promotes Russian culture, wrote on Facebook. 鈥淩elations have been poor for a long time, and the cultural field is the only arena where we can have positive, two-way reciprocal communication.鈥

Relations strained further on Friday when London鈥檚 Metropolitan Police said that it鈥檚 treating as murder the death of Nikolai Glushkov, a close associate of Putin opponent Boris Berezovsky — a one-time billionaire who was himself found hanged in 2013 in his house outside London.

Mr. Glushkov, 68, was found dead at his home in the southwest of the UK capital on March 12. An autopsy showed he died from 鈥渃ompression to the neck,鈥 the police said in a statement, adding that there was no evidence he had been poisoned or to link his death to the attack on the Skripals. — Bloomberg