British Prime Minister Theresa May on Saturday once again blamed Russia for its alleged role in a nerve agent attack against a former spy in England, warning that any state-sponsored attack on British soil would be met with consequences.

At the Conservative Party Spring Forum, she said her government had anticipated Russia’s decision earlier in the day to order the expulsion of 23 British diplomats as a tit-for-tat reaction to a similar move announced over Russia’s alleged hand in the attack with a weaponised nerve agent on ex-spy Sergei Skripal and his daughter Yulia, Efe reported.

“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,” May told the audience.

“We will never tolerate a threat to the life of British citizens and others on British soil from the Russian government,” the Conservative leader added, eliciting applause.

Britian has accused Russia of using a military grade, allegedly Soviet-produced nerve agent belonging to a strain known as Novichok against Sergei and Yulia, both of whom remained in a critical condition.

Russia’s Foreign Ministry spokeswomen Maria Zakharova on Saturday said the nerve agent had never been developed in the Soviet Union or Russia and said it was most likely from somewhere in western Europe.

Moscow officials have consistently denied having any knowledge of the alleged poisoning of Skripal, a former Russian army colonel who in 2004 was convicted of passing on state secrets to British intelligence, although later provided with asylum in Britain in a prisoner swap.

He and his daughter were found slumped over on a park bench in the southern English city of Salisbury on March 4.