Russia regrets the decision by Western governments to expel Russian diplomats over the poisoning of a former Russian double agent in Britain and Moscow's response will be based on the principle of reciprocity, the Kremlin spokesman said on Monday.

Dmitry Peskov told reporters President Vladimir Putin would make the final decision about how Russian responds to the expulsions, which were ordered over the nerve gas attack targeting former spy Sergei Skripal in the English city of Salisbury.

Russia denies Britain's charge that it was involved in the attack.