BRITISH Prime Minister Theresa May said Monday that Russia was “highly likely” responsible for the attempted murder of former Russian double agent Sergei Skripal and his daughter Yulia in the English city of Salisbury on March 4.

In a strongly worded statement to the House of Commons that is likely to plunge U.K.-Russia relations to a new low, May said the “military grade” nerve agent used in the attack had been identified as Novichok, a substance developed in the Soviet Union in the 1970s.

May said the Russian ambassador has been summoned to the U.K. Foreign Office to explain whether the attack was “a direct action by the Russian state,” or the result of the Russian Government “losing control” of its stock nerve agents.

May demanded a response from the Russian Government by the end of Tuesday. “Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian state against the United Kingdom,” May said.

“Based on the positive identification of this chemical agent by world-leading experts at the Defense Science and Technology Laboratory at Porton Down, our knowledge that Russia has previously produced this agent and would still be capable of doing so, Russia’s record of conducting state-sponsored assassinations, and our assessment that Russia views some defectors as legitimate targets for assassinations, the government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal,” May said.

Exactly how Britain might respond remains unclear. Possible options might include the expulsion of Russian diplomats and U.K.-based pro-Kremlin oligarchs, financial restrictions on figures linked to the Kremlin, and diplomatic efforts involving EU and U.S. allies.

White House press secretary Sarah Sanders described the episode as an outrage, calling it “reckless, indiscriminate and irresponsible,” though she refused to blame Russia for the attack.

Russian Foreign Ministry spokeswoman Maria Zakharova dismissed May’s comments, telling CNN: “This is a circus show in the British Parliament.”

“The conclusion is obvious,” she continued. “This is another information and political campaign based on provocation.”

Speaking from Moscow before May made her statement, Russian President Vladimir Putin said the U.K. should “get to the bottom” of what happened to the former spy in the English city of Salisbury before talking to him, according to the state-run RIA news agency.

(SD-Agencies)