LONDON, March 14. /TASS/. The United Kingdom will expel 23 Russian diplomats over the poisoning case of former Russian spy Sergey Skripal and his daughter Yulia, UK Prime Minister Theresa May told the parliament on Wednesday.

May noted that after the murder of former Federal Security Service officer Alexander Litvinenko in 2006 the UK kicked out four Russian diplomats. "Under the Vienna Convention, the United Kingdom will now expel 23 Russian diplomats," May said, claiming that they are "undeclared intelligence officers."

"They have just one week to leave," she said.

May stressed that this would be "the biggest single expulsion for over 30 years." "It reflects the fact that this is not the first time that the Russian State has acted against our country," she said.

On March 12, May gave Russia a 24-hour deadline to provide its clarification on the incident in Salisbury, warning that otherwise London would consider it to be "an unlawful use of force by the Russian state against the United Kingdom."

Russia has condemned London’s ultimatum. Foreign Minister Sergey Lavrov said that Moscow had nothing to do with the poisoning of Skripal and his daughter. He stressed that in accordance with the Chemical Weapons Convention, the United Kingdom had had to immediately contact the country suspected of using such a substance, providing it with access to the substance in question. According to Lavrov, the Convention stipulates that a response to such a request must be given within ten days.

Earlier on Wednesday, Lavrov said Moscow had not received the UK’s official request but in line with its commitments Moscow would give its response should such a request be sent.

Former Russian military intelligence (GRU) Colonel Sergey Skripal, 66, and his 33-year-old daughter Yulia on March 4 suffered from the effects of a nerve agent. They were found unconscious on a shopping mall bench in Salisbury, southern England. Both are now in hospital in critical condition.

In 2004, Russia’s Federal Security Service (FSB) arrested Skripal and later on, he was sentenced to 13 years in prison for high treason. Six years later, the former colonel was handed over to the US as part of a swap deal involving espionage suspects. Later that same year, Skripal settled down in Britain.

According to the UK PM, the nerve gas, known as Novichok, which was used for Skripal’s poisoning, had been developed in the Soviet Union.