Russia's Foreign Minister Sergei Lavrov said Tuesday that Moscow "has no connection" to a deadly nerve agent used to attack a former Russian spy and his daughter in the U.K.

Lavrov said Russia had requested access to the nerve agent used in the March 4 attack in Salisbury, England, but had been denied access "to materials related to the Skripal case," Reuters reported.

U.K. Prime Minister Theresa May said Monday that it was "highly likely" that Russia was responsible for the attempted murders of Sergei Skripal and his daughter Yulia.

Stressing that Russia had no connection to the poisoning, Lavrov said he expected London to reply to Moscow's request to open up the investigation as Yulia is a Russian citizen.

Lavrov's comments come after Russia was given a deadline — the end of Tuesday — to explain why a nerve agent, which the U.K. deemed to have been created in Russia, was used to poison the Skripals.

Calling it a "reckless and despicable act," May said Monday: "There are therefore only two plausible explanations for what happened in Salisbury on March 4. Either this was a direct act by the Russian state against our country. Or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others."

May said U.K. Foreign Secretary Boris Johnson had summoned the Russian ambassador to the Foreign and Commonwealth Office to explain why the nerve agent was used in the poisoning. Moscow has until the end of Tuesday to respond, she said.

May hinted that Britain is "ready to take much more extensive measures" against Russia, beyond the commonplace expulsion of diplomats, visa freezes and suspended security cooperation.

Offering his support to the U.K. government, the now-ex U.S. Secretary of State Rex Tillerson said Monday "the attempted murder of a private citizen on the soil of a sovereign nation" was never justified.

"And we are outraged that Russia appears to have again engaged in such behavior. From Ukraine to Syria — and now the U.K. — Russia continues to be an irresponsible force of instability in the world, acting with open disregard for the sovereignty of other states and the life of their citizens," he said in a statement.

France's President Emmanuel Macron and the European Union have also offered the U.K. their support.