The UK will expel 23 Russian diplomats over the poisoning of former double agent Sergei Skripal and his daughter Yulia in the single biggest expulsion in more than 30 years.

Russia responded on Wednesday by calling London's move "an unprecedentedly crude provocation".

Theresa May, the UK prime minister, said Moscow reacted with "complete disdain" to a deadline issued on Monday for it to provide an explanation on how a Russia-made nerve agent ended up in Salisbury, in southern England, where the attack occurred.

"They have treated the use of a military-grade nerve agent in Europe with sarcasm, contempt and defiance," May said in parliament.

"There is no alternative conclusion other than that the Russian state was culpable for the attempted murder of Mr Skripal and his daughter, and for threatening the lives of other British citizens in Salisbury."

Skripal, 66, and his daughter Yulia, 33, were found unconscious on a bench outside a shopping centre in Salisbury on March 4, after they were poisoned. The two remain in critical condition in a hospital.

A former double agent, Skripal betrayed dozens of Russian agents to British intelligence before his arrest in Moscow in 2004. He was later sent to the UK in exchange for captured Russian spies.

'Hostile action'

May announced a range of responses to the alleged murder attempt, including withdrawal of an invitation to Sergey Lavrov, the Russian foreign minister, to visit the UK.

Cabinet ministers and members of the royal family would not attend the World Cup in Russia this summer.

May said the expelled diplomats were identified as "undeclared intelligence officers" and were given one week to leave the country.

Proposals for new legislation to "harden our defences" against "all forms of hostile state activity" would be developed urgently, May said.

She also announced plans to increase checks on private flights, customs and freight, and freeze Russian state assets where there is evidence they may be used to threaten the life or property of UK nationals or residents.

The Russian embassy in London called the expulsion of diplomats a "hostile action" that was "totally unacceptable, unjustified and shortsighted".

In a statement, the embassy said Alexander Yakovenko, Russia's ambassador, had been summoned to the UK's foreign office where he was informed of the punitive measures.

"We consider it categorically unacceptable and unworthy that the British government, in its unseemly political aims, further seriously aggravated relations," Russia's foreign ministry said in statement.

"Obviously, by using one-sided and non-transparent methods to investigate this incident, the British authorities are trying to concoct yet another unfounded anti-Russian campaign. Naturally, our countermeasures won’t keep you waiting."

Tit-for-tat game

Mathieu Boulegue, a Russia specialist at the UK-based Chatham House Institute of International Affairs, said May's announcement on Wednesday was a mixture of "business as usual, and showing a bit of teeth".

"In a way it is quite mild... I would have expected the reaction to have been stronger with more international traction gathered by the UK beforehand," Boulegue told Al Jazeera.

"Moving forwards, the key issue will be how Russia responds [and] whether it gets involved in a tit-for-tat game of sanctions and expulsions with the UK will determine who has the last word."

The US sided with the UK at a UN Security Council meeting called on Wednesday to discuss the attempted assassination.

"The United States believes that Russia is responsible for the attack on two people in the United Kingdom using a military-grade nerve agent," US Ambassador Nikki Haley told the meeting.

The poisoning of Skripal and his daughter has drawn comparisons to the murder of Alexander Litvinenko in 2006.

The former Russian spy died three weeks after drinking green tea laced with radioactive polonium-210 at London's Millennium Hotel. Russia denied involvement in the 43-year-old death.

A British inquiry said in January 2016 that Moscow had "probably" ordered the poisoning of Litvinenko, who lived in exile in Britain.