March 13 (UPI) -- The Russian government is facing a midnight deadline to furnish answers about the poisoning of a former Kremlin intelligence agent, but it denies it knows anything.
British Prime Minister Theresa May said she wants answers by the end of the day and U.S. Secretary of State Rex Tillerson condemned the act and said there should be "serious consequences" for Moscow.
May demanded to know why a Russian-made nerve agent was used in the poisoning of former Russian agent Sergei Skripal and his daughter earlier this month. Skripal, 66, and daughter Yulia Skripal, 33, were found slumped on a bench following the attack and remain in critical condition, officials said.
May said Monday it was "highly likely" Moscow was responsible for the March 4 attack in Salisbury, Wiltshire, because the poison was part of a group of military-grade nerve agents -- known as Novichok -- developed by Russia.
"Either this was a direct action by the Russian state against our country, or the Russian government lost control of its potentially catastrophically damaging nerve agent and allowed it to get into the hands of others," she said.
A statement from the White House said President Donald Trump spoke with May on Tuesday and offered assistance in Britain's investigation.
"President Trump agreed with Prime Minister May that the government of the Russian Federation must provide unambiguous answers regarding how this chemical weapon, developed in Russia, came to be used in the United Kingdom. The two leaders agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms."
Tillerson spoke to British Foreign Secretary Boris Johnson on Tuesday and said the agent was "only in the hands of a very, very limited number of parties" and it is "beyond comprehension" that a government official would use such a dangerous substance in a public place.
Russia repeatedly denied claims it was involved in Skripal's poisoning. Russian foreign ministry spokeswoman Maria Zakharova said May's statement is "a circus show in the British Parliament."
"It's another political information campaign, based on a provocation," she added.
Sergei Lavrov, Russia's foreign minister said, "Russia is not responsible."
Lavrov suggested Moscow would not comply with the deadline and called out Britain for turning down Moscow's request to see samples of the nerve agent, something the foreign minister said was a violation of the international Chemical Weapons Convention.
May said Russia's British ambassador has been summoned to "explain which of these two possibilities it is" and warned if there was no "credible response" by the end of Tuesday, the conclusion would be made that there was an "unlawful use of force" by Moscow.
Depending on the response, May said Britain must "stand ready to take much more extensive measures" against Russia -- and that they would be detailed by government officials Wednesday.