LONDON — Britain announced Wednesday it will expel 23 Russian diplomats — the biggest such expulsion since the Cold War — and break off high-level contacts with the Kremlin over the nerve-agent attack on a former spy and his daughter in an English town.

Prime Minister Theresa May told lawmakers that the 23 diplomats, who have been identified as undeclared intelligence officers, have a week to leave.

She announced a range of economic and diplomatic measures, including the suspension of high-level bilateral contacts with Russia. An invitation for Russian Foreign Minister Sergey Lavrov to visit Britain has been canceled, and May said British ministers and royals will not attend the soccer World Cup in Russia this summer.

May said Britain would also introduce new measures to strengthen defenses against hostile state activities, freeze Russian state assets wherever there was evidence of a threat.

May announced the measures after Moscow ignored a midnight deadline to explain how a nerve agent developed by the Soviet Union was used against Sergei and Yulia Skripal. The father and daughter remain in critical condition in a hospital in Salisbury, southwestern England.

Russia’s Embassy in London on Wednesday condemned as “hostile action” the series of punitive measures.

“We consider this hostile action as totally unacceptable, unjustified and shortsighted. All the responsibility for the deterioration of the Russia-UK relationship lies with the current political leadership of Britain,” the embassy said in a statement.

Russia’s ambassador in London, Alexander Yakovenko, said Britain’s actions were “ absolutely unacceptable” and “ a provocation.”

Putin spokesman Dmitry Peskov told reporters on Wednesday that Russia “ rejects the language of ultimatums.”

European Union leaders will discuss Russia’s role in the nerve agent attack in Britain when they meet May next week, summit chair Donald Tusk said on Wednesday. — Agencies