(CNN) Detectives with London's Metropolitan Police said Wednesday they believe former Russian double agent Sergei Skripal and his daughter first came into contact with a nerve agent at Sergei Skripal's home, and police have identified the highest concentration of the nerve agent to date as being on the home's front door. 
 
 The pair were poisoned March 4 after being exposed to what British police believe was a military-grade nerve agent. They are hospitalized in critical condition. 
 
 Skripal and his daughter, Yulia, were found slumped on a bench in an outdoor shopping complex in Salisbury, England. They had no visible injuries, according to police. 
 
 They were near a number of restaurants, one of which was closed as part of the initial investigation. 
 
 Detectives now plan to focus their investigation around Sergei Skripal's Salisbury home for the coming weeks and possibly months, the Met Police said. Yulia Skripal was visiting her father. 
 
 Police also plan to search the surrounding area. 
 
 Yulia Skripal 
 
 "Those living in the Skripals' neighborhood can expect to see officers carrying out searches as part of this, but I want to reassure them that the risk remains low and our searches are precautionary," Deputy Assistant Commissioner Dean Haydon said in a statement. 
 
 Around 250 counterterrorism detectives are working around the clock on the investigation, the Met Police said, adding it is one of the largest and most complex investigations undertaken by British counterterrorism police. 
 
 Officers are examining more than 5,000 hours of closed-circuit television and more than 1,350 seized items, police said. They have identified around 500 witnesses and taken hundreds of statements. 
 
 Detectives have found traces of the nerve agent at other scenes in the past few weeks but at lower concentrations than at the home address, the Met Police said. 
 
 Surveillance footage shows Sergei Skripal shopping at a convenience store days before he was poisoned. 
 
 Diplomatic fallout 
 
 The UK has expelled 23 Russian diplomats over the poisoning of the Skripals, which it blames on Moscow. Russia denies it was involved and has suggested the UK could be behind it. 
 
 In a show of support for Britain, more than 20 other countries have kicked out Russian diplomats . Those countries include the United States, Canada, Australia and 18 European Union states. 
 
 In a speech Wednesday evening, British Foreign Minister Boris Johnson thanked the countries "from the bottom of my heart" for standing with Britain, saying they did it despite the risk of retaliation. 
 
 "I believe that these expulsions represent a moment when a feeling has suddenly crystallized, when years of vexation and provocation have worn collective patience to (the) breaking point, and when across the world -- across three continents -- there are countries who are willing to say enough is enough," Johnson said at an annual gathering of the diplomatic corps in London. 
 
 Russian Foreign Minister Sergey Lavrov said the United States pressured and blackmailed other countries to expel Russian diplomats. 
 
 British Prime Minister Theresa May speaks Monday in Parliament. 
 
 Moscow has already responded by expelling 23 British diplomats and shuttering British cultural institutions in Russia. Tuesday, Lavrov warned of further retaliation , saying, "Rest assured, we will respond," according to state media. 
 
 Russia's ambassador to Australia called the expulsions "unfair." 
 
 "It's rather like the beginning of 'Crime and Punishment,'" Johnson said. "We're all confident of the culprit, and the only question is whether he will first confess or be caught." 
 
 The Skripals 'may never fully recover' 
 
 According to the UK, the Skripals were exposed to a Soviet-era nerve agent known as Novichok, a colorless, odorless and tasteless liquid described as one of the world's most sophisticated and deadly chemical weapons. 
 
 While British officials have said they believe the public health risk is low, Prime Minister Theresa May has also said more than 130 people in Salisbury could have been exposed to the nerve agent. 
 
 May said Monday that doctors have indicated the Skripals may never fully recover. 
 
 "This shows the utterly barbaric nature of this act and the dangers that hundreds of innocent citizens in Salisbury could have faced," May said. 
 
 Johnson said Wednesday that the Kremlin underestimated the global response to the poisoning. 
 
 "If they thought that the world had become so hardened and so cynical as not to care about the use of chemical weapons in a place like Salisbury," he said, "if they believed that no one would give a fig about the suffering of Sergei and Yulia Skripal, or that we would be indifferent to the reckless and contemptuous disregard for public safety ... then this is their answer." ||||| Image copyright EPA/ Yulia Skripal/Facebook Image caption Sergei Skripal, 66, and his daughter Yulia, 33 were poisoned by a nerve agent called Novichok 
 
 Yulia Skripal, the daughter of ex-spy Sergei Skripal, is improving rapidly and no longer in a critical condition, says the hospital treating her. 
 
 She and her father were admitted nearly four weeks ago after being exposed to a nerve agent in Salisbury. 
 
 The BBC understands from separate sources that Ms Skripal is conscious and talking. 
 
 However Mr Skripal remains in a critical but stable condition, Salisbury District Hospital said. 
 
 Doctors said Ms Skripal, "has responded well to treatment but continues to receive expert clinical care 24 hours a day". 
 
 "I want to take this opportunity to once again thank the staff of Salisbury District Hospital for delivering such high quality care to these patients over the last few weeks," said Dr Christine Blanshard, Medical Director for Salisbury District Hospital. 
 
 "I am very proud both of our front-line staff and all those who support them." 
 
 BBC correspondent Duncan Kennedy says a corner appears to have been turned for Yulia Skripal, who is now in a stable condition. 
 
 However there is no news on what the long-term damage might be, he adds. 
 
 Meanwhile the police have placed cordons round a children's play area at Montgomery Gardens near Mr Skripal's home. 
 
 "Officers will be searching it as a precautionary measure," said Deputy Assistant Commissioner Dean Haydon. 
 
 The Skripals were admitted to hospital on 4 March after being found collapsed on a bench at the Maltings shopping centre in Salisbury. 
 
 Police have been treating the case as attempted murder. 
 
 On Wednesday, police said the Skripals first came into contact with the nerve agent at the former Russian spy's home in Salisbury. 
 
 Image copyright EPA Image caption Police stand outside the house believed to be the home of Sergei Skripal 
 
 Forensic tests show the highest concentration was found on the front door. 
 
 The nerve agent was found at other locations in the town but in lower concentrations, the Metropolitan Police said. 
 
 A police officer who fell seriously ill after responding to the attack - Det Sgt Nick Bailey - was treated in hospital but was discharged on 22 March. 
 
 DS Bailey, who is believed to have visited Mr Skripal's house after the incident has spoken of his ordeal, saying: "Normal life for me will probably never be the same." 
 
 The British government has accused the Russian state of involvement in the attack - a claim Moscow has denied. 
 
 Prime Minister Theresa May said the chemical used had been identified as being part of a group of nerve agents developed by Russia known as Novichok. 
 
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 In response to the incident, Mrs May announced a series of sanctions including the expulsion of 23 Russian diplomats. 
 
 As a counter-measure the Kremlin said it would expel an equal number of British diplomats from Russia and close down the country's British Council. 
 
 Then - in what is believed to be the largest collective expulsion of Russian intelligence officers in history - more than 20 governments expelled diplomats in their countries, including the US, which removed 60. 
 
 In reply, Russia will expel 60 US diplomats and the US consulate general in St Petersburg is to be closed. ||||| New York (CNN) Russia, at a United Nations Security Council meeting, warned the British government Thursday it was "playing with fire" with accusations that Moscow was behind the poisoning of a Russian former spy and his daughter in the United Kingdom. 
 
 Russia's UN Ambassador Vassily Nebenzia blasted the UK, calling the allegations against Russia a "fake story." 
 
 The Russian UN diplomat warned "we have told our British colleagues that they are playing with fire and they will be sorry." 
 
 Asked after the meeting what he meant by saying the UK would be sorry, Nebenzi replied that if the UK's accusation was untrue, "a normal person should be sorry for that." 
 
 He accused the United Kingdom of turning other countries against Russia. 
 
 "You started a wave that even reached New York," he said. 
 
 Moscow, emboldened after the UK was forced to withdraw a claim that its scientists had pinned the blame on Russia for the attack, further attempted to embarrass Britain in front of its international allies. 
 
 But the UN ambassador from the UK, Karen Pierce, said she would not be lectured by Russia, which she said had blocked inquiries into the use of chemical weapons in Syria. 
 
 "Everything we have done ... has been consistent with the Convention on Chemical Weapons," she said. 
 
 Russia refused to help when the UK asked early in the investigation, Pierce said. 
 
 Pierce told the Council "we all know why that investigation is underway. It's because a military-grade nerve agent was used in an attempt to kill civilians on British soil. It was carried out recklessly and it was carried out without regard for public safety." 
 
 She questioned the need for Thursday's meeting, saying the chemical weapons watchdog, the Organization for the Prohibition of Chemical Weapons, has yet to release its report on the incident. 
 
 Battle of barbs continues 
 
 A month after former Russian double agent Sergei Skripal and his daughter Yulia were poisoned in the English city of Salisbury, the United Kingdom and Russia remain locked in a battle over who is to blame. 
 
 UK Prime Minister Theresa May has said it was "highly likely" the attack was ordered by the Russian government. The Kremlin has repeatedly denied the accusation. Russian Foreign Minister Sergey Lavrov said Thursday that the affair was a "pretext" for the expulsion of Russian diplomats around the world. 
 
 On Wednesday, Moscow failed in its efforts to persuade OPCW to allow a joint UK-Russia investigation into the attack. The OPCW is already carrying out an independent investigation at the UK's request, and expects to receive the results of its analysis within a week. Britain is also carrying out its own inquiry, with support from the OPCW. 
 
 Attention has turned to the United Nations. It was the second time the Security Council discussed the poisoning. At a March 15 meeting that was called by the UK, US Ambassador to the United Nations Nikki Haley blasted the Russian government for the attack and called for a firm international response. 
 
 Skripal, 66, and his daughter Yulia, 33, remain in Salisbury District Hospital following the attack on March 4. Sergei Skripal is described as in a critical but stable condition. 
 
 Yulia Skripal announced Thursday that she had woken up "over a week ago" and that her "strength is growing daily." 
 
 "I am grateful for the interest in me and for the many messages of goodwill that I have received," Skripal said in a statement released on her behalf by London's Metropolitan Police. 
 
 "I have many people to thank for my recovery and would especially like to mention the people of Salisbury that came to my aid when my father and I were incapacitated. Further than that, I would like to thank the staff at Salisbury District Hospital for their care and professionalism," she said. 
 
 "I am sure you appreciate that the entire episode is somewhat disorientating, and I hope that you'll respect my privacy and that of my family during the period of my convalescence," she added. 
 
 Pierce said the UK has relayed a request for a visit from a Russian consular official to Skripal. 
 
 "We await her response," Pierce said. 
 
 A Russian state television station reported Thursday that Viktoria Skripal, the cousin of Yulia Skripal, said she had spoken to Yulia by phone. 
 
 UK experts believe the Skripals were poisoned with a Russian-made nerve agent, Novichok 
 
 The Times of London, citing unnamed sources, reported on Thursday that UK security services had pinpointed the location of the Russian laboratory that manufactured the nerve agent. 
 
 Putin: Common sense must prevail 
 
 On Wednesday, speaking at a trilateral summit with Turkey and Iran, Russian President Vladimir Putin told reporters he wanted to see "a healthy political process" based on international law. 
 
 "We are not expecting anything but common sense to prevail; international relations will not tolerate the recent damage done," he said. 
 
 The UK expelled 23 Russian diplomats in the wake of the attack, sparking a wave of similar moves by UK allies around the world. The US expelled 60 Russian diplomats as part of the international effort. Moscow responded by kicking out diplomats from at least 23 countries , including 60 American diplomats. It also ordered the closure of the US consulate in St. Petersburg. 
 
 Lavrov said Thursday that Russia wants "to find the truth" about the poisoning in Salisbury and that "provocations are being arranged" in the Skripal case to demonize Russia. 
 
 He claimed that many countries had been pressured into supporting the UK and described the mass expulsion of Russian diplomats as "an open mocking of diplomatic ethics" that had not seen for a long time. 
 
 Russian Ambassador to the United Kingdom Alexander Yakovenko told a news conference Thursday that Russia has "no information about Yulia Skripal, we don't know about Sergei." 
 
 Speaking to reporters at the Russian Embassy in London, Yakovenko said Yulia's cousin Viktoria was "waiting for the visa in Moscow, a British visa. We will see what will be the outcome of that visit." 
 
 He repeated Russia's complaint that Britain is not allowing it access to its citizens, Sergei and Yulia Skripal, or to the British investigation into their poisoning. The UK government must be "transparent" about the evidence, he said. 
 
 Yakovenko said Russia would accept the result of the OPCW investigation -- but suggested that its validity would depend on which nations' experts were involved. "These results should be confirmed by the international community, so we want to see who are the experts," he said. 
 
 Questions around nerve agent's source 
 
 Questions continue to dog the investigation into the attack on the Skripals, who were found slumped on a bench at an outdoor shopping complex in Salisbury. UK police believe they came into contact with the military-grade nerve agent on Skripal's front door. 
 
 On Tuesday, UK scientists said that while they had identified the nerve agent as Novichok, they were unable to say exactly where it had been manufactured. 
 
 "We have not identified the precise source, but we have provided the scientific info to government, who have then used a number of other sources to piece together the conclusions you have come to," Gary Aitkenhead, chief executive of the UK government laboratory at Porton Down, told Sky News on Tuesday. 
 
 Further complicating the picture, the UK Foreign Office confirmed on Wednesday it had deleted a tweet that claimed that British chemical weapons experts believed Russia had produced the nerve agent. The Foreign Office said the tweet was "truncated and did not accurately report" a briefing by the British ambassador to Moscow last month. 
 
 The British government says the scientific analysis from Porton Down forms only part of the picture. It insists that only Russia had the capability to carry out the attack, that Moscow had identified former double agents as legitimate targets, and was known for its involvement in state-sponsored attacks in the past. 
 
 In its report on Thursday, the Times of London cited security sources claiming that the location for the manufacture of the Novichok had been identified "using scientific analysis and intelligence in the days after the attempted murder of Sergei and Yulia Skripal a month ago." 
 
 The Times said security sources didn't have "100% certainty" but there was a high degree of confidence in the location. The UK government had known about the facility's existence before the attack on March 4, it added. 
 
 The UK Foreign Office refused to comment on The Times' report. "We have nothing more to add to that story," a spokesman told CNN.
– The military-grade nerve agent that left former Russian double agent Sergei Skripal and his daughter near death appears to have been left on his front door in Salisbury, England, police say. Investigators say the Skripals first came into contact with the nerve agent at Skripal's home, and the highest concentration of it was found on the door, the Guardian reports. Skripal and his daughter, Yulia, were found unconscious on a bench at an outdoor shopping complex on March 4. Detective Sergeant Nick Bailey, who was hospitalized for more than two weeks after the incident, is believed to have become sick after visiting the Skripal house, where he was one of the first on the scene, reports the Telegraph. Police say residents of Skripal's neighborhood can expect more searches in the area, but "the risk remains low." Britain blames Russia for the attack. It has expelled 23 Russian diplomats and numerous other countries, including the US, have followed suit. In a speech late Wednesday, British Foreign Secretary Boris Johnson thanked Britain's allies "from the bottom of his heart," CNN reports. "I believe that these expulsions represent a moment when a feeling has suddenly crystallized, when years of vexation and provocation have worn collective patience to (the) breaking point, and when across the world—across three continents—there are countries who are willing to say enough is enough," he said. (A relative says there is almost no chance the Skripals will survive.)