Russia will not respond to UK Prime Minister Theresa May's demand for an explanation over the poisoning of ex-spy Sergei Skripal in Salisbury until it has a sample of the toxin. May's deadline expired on Wednesday at midnight.

The Russian embassy in the UK backed Foreign Minister Sergey Lavrov's earlier statement that Moscow would not respond to London's ultimatum unless the internationally-accepted procedure is followed in the investigation. The case must go through the proper channels of the Organization for the Prohibition of Chemical Weapons (OPCW), of which both Russia and the UK are members, Lavrov said on Tuesday. The OPCW rules allow London to send a formal inquiry to Moscow, with a 10-day window for a reply.

Moscow sent a request for a sample of the purported chemical agent as soon as allegations of its Soviet origins surfaced, Lavrov said. Those requests have been ignored by London. “Russia will not respond to London’s ultimatum until it receives samples of the chemical substance,” an embassy spokesman told Reuters as the deadline expired.

Read more

In a Tuesday statement addressed to the OPCW, the Russian embassy called the ultimatum's format “absolutely unacceptable” and decried UK officials' "vicious attacks" against Moscow.

"Our British colleagues should save their propaganda fervour and slogans for their unenlightened domestic audience, where perhaps they will have some effect. Here, within the walls of a specialised international organisation, such as the OPCW, one must use facts and nothing but the facts. Stop fomenting hysteria, go ahead and officially formalise your request to begin consultations with us in order to clarify the situation. A fair warning, we will require material evidence of the alleged Russian trace in this high-profile case," the statement reads.

Russia has also asked to be granted access to all materials from the ongoing investigation, since one of the victims, Yulia Skripal, the daughter of the 66-year-old former spy, is a Russian citizen, according to Lavrov.

Moscow dismissed the allegations of the double poisoning, with Russian Foreign Ministry spokesperson Maria Zakharova dubbing the hearing in the British Parliament as “a circus show.” Zakharova warned against “creating new fairy tales,” and pointed to the lack of evidence in other high-profile cases London had linked to the Kremlin in the past.

On Monday, May said Skripal and his daughter were poisoned with a secret Soviet-made chemical weapon named Novichok. She gave Russia 36 hours to come up with an explanation and said that the UK would otherwise default to holding Russia responsible. According to May, only two explanations are possible: either Moscow poisoned the former spy on purpose, or allowed its nerve agent to get into the wrong hands.

While May was comparatively careful with her wording, saying it was only "highly likely" that Russia is to blame for the poisoning, some of the MPs she was addressing went all-out. Their condemnations ranged from referencing Hitler's Nazi Germany, to accusing Russia of "warlike acts," to blaming Vladimir Putin for terrorist attacks on Russian soil.