MOSCOW (Reuters) - Russia will respond to the mass expulsion of Russian diplomats by Western countries in kind, Valentina Matviyenko, the speaker of the upper house of parliament, said on Wednesday, the RIA news agency reported.

It cited her as telling reporters: “Without a doubt, Russia, as is diplomatic practice, will respond symmetrically and observe parity when it comes to the number of diplomats.”

Ties between London and Moscow are badly strained by the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in Salisbury. Britain alleges Russia was to blame, but Moscow says it had no involvement.

The United States said on Monday it would expel 60 Russian diplomats, joining governments across Europe in punishing the Kremlin for the nerve agent attack.