UK never tolerates threat to life of citizens, others on its soil: May

"We will never tolerate a threat to the life of British citizens and others on British soil from the Russian Government," British Prime Minister Theresa May said after Russia announced to expel 23 British diplomats on Saturday.

She said that the British government "has anticipated a response of this kind" and will consider its next steps in coming days, "alongside our allies and partners".

A spokesperson of British Foreign and Commonwealth Office said: "In light of Russia's previous behaviour, we anticipated a response of this kind and the National Security Council will meet early next week to consider next steps. Our priority today is looking after our staff in Russia and assisting those that will return to the UK."

"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 spokesperson added.

The Russian Foreign Ministry expelled 23 British diplomats on Saturday in a retaliatory move over British punitive measures against Russia and the former Russian spy attack row.

"A total of 23 diplomatic employees of the British Embassy in Moscow are declared personae non gratae and must leave within a week," said the statement, warning that Moscow retained the right to respond if Britain continues to take unfriendly steps against Russia.

It also said it would close the British Consulate-General in St Petersburg and close the British Council in Moscow.

Sergei Skripal, a former Russian intelligence officer, and his 33-year-old daughter Yulia Skripal were found unconscious on a bench at a shopping center in Salisbury, Wiltshire last week, and remain still in critical condition, according to reports.

The British government said they were poisoned with Novichok, a nerve agent of a type developed by Russia.

The Russian government has denied any involvement in the attack.