British Prime Minister Theresa May gave on Monday Russia until the end of Tuesday to explain a nerve agents program allegedly involved in the poisoning of a former Russian spy. "It is highly likely that Russia was responsible for the act against Sergei and (his daughter) Yulia Skripal," May said. She said that the military-grade nerve agent used in the attack was of a type developed by Russia. She spoke in the House of Commons after she chaired a National Security Council meeting to hear the latest evidence in the case. "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," the prime minister added. May stopped short of announcing retaliatory measures against Moscow and instead gave the Kremlin until the end of Tuesday to disclose details of the Novichok nerve agents program to the Organization for the Prohibition of Chemical Weapons. The organization is the implementing body of the Chemical Weapons Convention, which entered into force in 1997 and has 192 member states. The nerve agent used in the March 4 attack in the southwestern city of Salisbury was identified by experts at a British army base, while May said Russia had a record of "state-sponsored assassinations". "This attempted murder using a weapons-grade nerve agent in a British town was not just a crime against the Skripals," she told lawmakers. "It was an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk. And we will not tolerate such a brazen attempt to murder innocent civilians on our soil," May concluded. Moscow was quick to reject Mays statement, saying it was part of an "information and political campaign based on provocation." Russian foreign ministry spokeswoman Maria Zakharova said: “This is a circus show in the British parliament.” "Rather than think up new fairytales, maybe someone in the kingdom could explain how the previous ones ended up -- about Litvinenko, Berezovsky, Perepilichnyy and many others who have mysteriously died on British soil," Zakharova said. Former spy Alexander Litvinenko, oligarch Boris Berezovsky and whistleblower Alexander Perepilichnyy all died in the UK in recent years. The Kremlin has long rejected any involvement in their deaths, despite a British judge concluding Russian President Vladimir Putin likely approved Litvinenkos killing. Putin spokesman Dmitry Peskov told reporters that Skripal worked for British intelligence and was poisoned on British soil, and therefore the incident "has nothing to do with Russia, let alone the Russian leadership." Peskov also said the Kremlin hasnt heard any official statements of Russian involvement. Skripal was a Russian military intelligence officer when he was recruited to spy for Britain in the 1990s. He was jailed in Russia in 2006 for revealing state secrets before being freed in a spy swap in 2010. He had settled in the cathedral city of Salisbury, 90 miles (140 kilometers) southwest of London. He and his daughter were found comatose on a bench near the city center after visiting an Italian restaurant and a pub.