Moscow, Mar 17 (IANS): Russia on Saturday announced expulsion of 23 British diplomats amid tensions over the nerve agent attack on an ex-spy and his daughter in the UK.

The move by the Russian Foreign Ministry came in response to Britain's decision to expel 23 Russian diplomats.

It said 23 diplomatic staff at the UK Embassy in Moscow would be "declared persona non-grata" and expelled within a week, Sputnik news agency reported.

They were ordered to leave over the incident in Salisbury which the UK government blamed on Russia.

Russian Foreign Ministry summoned UK Ambassador to the country Laurie Bristow to inform him about Moscow's retaliation over Britain's decision to expel Russian diplomats.

Former Russian spy who became a double agent for Britain, Sergei V. Skripal, 66, and his daughter Yulia, 33, remain critically ill in hospital, after they were found unconscious on a bench in the Wiltshire city on March 4.

Skripal, who is a retired Russian military intelligence officer, was jailed for 13 years by Russia in 2006 for spying for Britain.

The UK government said they were poisoned with a nerve agent of a type developed by Russia called Novichok and Prime Minister Theresa May said she believed Moscow was "culpable".