British Prime Minister Theresa May said that it was “highly likely” that the Russian government was behind the attempted assassination of a former Russian military intelligence officer turned spy for Britain’s MI6 on March 4th.

“It is now clear that Mr. Skripal and his daughter were poisoned with a military-grade nerve agent of a type developed by Russia,” May said in the House of Commons. “The government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal.”

She went on to say that, either the incident was a “direct act of the Russian state against our country,” or evidence that Russia failed to maintain control over its arsenal of banned nerve agents. As a result, the Prime Minister explained, the Russian ambassador has been summoned, stating that she and the UK government are demanding an explanation by the end of the day on 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, and I will come back to this House and set out the full range of measures we will take in response,” May said.

“We shall not tolerate such a brazen act to murder innocent civilians on our soil.”

According to Prime Minister May, the nerve agent in question belongs to a family of poisons called “Novichok,” (Russian: новичок) which is roughly translated as “newcomer”, “newbie” or “new guy.” It was produced in large quantities by the Soviet Union in the 1970s and 80s, and had a fearsome reputation among U.S. researchers and analysts. According to the testimony of Vil Mirzayanov, one of the chemists that helped develop the toxin prior to the fall of the Soviet Union, Russia retained a stockpile of the agent large enough to kill “hundreds of thousands of people.”

23 Russian diplomats are ousted from the United Kingdom

Read Next: 23 Russian diplomats are ousted from the United Kingdom

The incident May referred to took place on March 4th in the British town of Salisbury, where Sergei Skripal, 66, and his daughter were found unconscious on a bench in the shopping district of the city center. The two were hospitalized and have remained in critical condition ever since, while law enforcement, emergency services, and eventually, hundreds of troops descended upon the scene to manage the cleanup effort that was labeled a “major incident” by UK authorities.

Skripal had formerly served as a Colonel in Russian military intelligence before selling the names of Russian operatives conducting clandestine operations in the UK to MI6 for a reported $100,000. Skripal pled guilty to treason and was sentenced to 13 years in prison by Russian courts in 2006, but was granted asylum to the UK following a prisoner transfer brokered by the United States that saw the return of captured Russian spies, and the release of a handful of spies that had done work for American or British intelligence services.

“Traitors will kick the bucket,” Vladimir Putin said in an interview following Skripal’s release in 2010. “Trust me. These people betrayed their friends, their brothers in arms. Whatever they got in exchange for it, those thirty pieces silver they were given, they will choke on them.”

Despite the use of a toxin that can be directly traced back to the Russian government, the Kremlin has denied any involvement in the incident, echoing a similar incident that took place in 2006, wherein another former Russian spy, Alexander Litvinenko, was killed using a rare radioactive isotope called polonium-210 linked to Russia’s nuclear weapons program.

Military forces work on a van in Winterslow, England, Monday, March 12, 2018, as investigations continue into the nerve-agent poisoning of Russian ex-spy Sergei Skripal and his daughter Yulia, in Salisbury, England, on Sunday March 4,2018. | AP Photo/Frank Augstein

Russian Foreign Ministry spokeswoman Maria Zakharova said Monday’s statement by Theresa May was, “a circus show in the British parliament.”

“The conclusion is obvious — it’s another information and political campaign based on provocation,” she said.

Vladimir Dzhabarov, first deputy head of the Federation Council’s foreign affairs committee, echoed those sentiments by claiming that Skripal posed no threat to Russian security, arguing that there would be no value in eliminating the former spy.

“This already is not our issue,” Mr. Dzhabarov told Interfax. “He had access neither to our secrets nor facilities. He was of no use to us, to Russia in general.”

In an interview following his release in 2010, however, Skripal himself contested the idea that Moscow would forget about his betrayal. According to him, the FSB, the successor to the infamous KGB, would not rest until they had exacted revenge.

“They will try to shoot me in the back of the head, but they might use poison,” he said in an interview. “They never forget. When I was at the KGB in the 1970s they were still chasing people who had betrayed them 30 years before.”

Image courtesy of the Associated Press