LONDON — Moscow faces a midnight on Tuesday deadline to tell London how a Russian-made nerve agent came to be used in the brazen poisoning of a former double agent in Britain, with Prime Minister Theresa May threatening “a full range of measures” in retaliation. Russia has denied accusations of its involvement in the attack on Sergei Skripal and his daughter in an English city on March 4, as the US, NATO and the European Union all backed Britain in the deepening diplomatic row. Meanwhile, Russia on Tuesday rejected Britain’s demand and said London should provide Moscow with access to the nerve agent. “Before giving ultimatums it’s better to honor your own obligations on international law,” Lavrov told reporters, referring to the Chemical Weapons Convention. Russia’s top diplomat said that Britain should have sent Moscow an official request about the substance used on its soil. Lavrov said Russia had not received such a request and also demanded to be given access to the Russian-made nerve agent used to poison former double agent. “Through an official note we had demanded access to this substance,” Lavrov said, adding that Russia also asked to be informed about the investigation. “Our requests have been denied.” “If the procedures stipulated by the convention will be implemented I assure you that Russia will fulfill its obligations,” Lavrov said. British Prime Minister Theresa May told parliament it was “highly likely” Moscow was behind the poisoning, giving Russia until the end of Tuesday to answer the accusations. Foreign Secretary Boris Johnson said the attack was the “first use of nerve agent on the continent of Europe since the end of the Second World War” and vowed that Britain’s response if it concludes Russia was responsible would be “commensurate but robust”. May has said that her government was considering a British version of the US “Magnitsky Act”, which was adopted in 2012 to punish Russian officials accused of human rights violations. Skripal, 66, and his daughter Yulia, 33, remain in a critical condition in hospital after being found unconscious on a bench outside a shopping center in the southwestern city of Salisbury. Emergency workers in biohazard suits have been deployed in the normally sleepy city, while about 500 people who may have come into minimal contact with the nerve agent were urged to wash clothes and belongings as a precaution. US Secretary of State Rex Tillerson said Washington has “full confidence” in the British investigation, adding that it was “almost beyond comprehension” that a state would use such a dangerous substance on public streets. “We agree that those responsible — both those who committed the crime and those who ordered it — must face appropriately serious consequences,” he told reporters. “We stand in solidarity with our allies in the United Kingdom and will continue to coordinate closely our responses.” May warned that if there was “no credible response” Britain will conclude it was “an unlawful use of force by the Russian State against the UK”. The Daily Telegraph newspaper reported that Britain was consulting allies in NATO about possibly invoking its Article 5 principle of common defence. NATO Secretary General Jens Stoltenberg said the incident was “of great concern” while European Commission Vice President Valdis Dombrovskis said Britain could “count on EU solidarity in this regard.” — AFP