Media playback is unsupported on your device Media caption "Our quarrel is with Putin's Kremlin," Boris Johnson says. 
 
 Russian President Vladimir Putin is "overwhelmingly likely" to have ordered the nerve agent attack on an ex-spy and his daughter, Boris Johnson has said. 
 
 The foreign secretary said "our quarrel is with Putin's Kremlin, and with his decision" over the Salisbury incident. 
 
 Russia denies involvement and said the accusations against Mr Putin were "shocking and unforgivable". 
 
 Meanwhile, the head of Nato told the BBC that Russia has underestimated the "resolve and unity" of the UK's allies. 
 
 Speaking during a visit to a west London military museum with the Polish foreign minister, Mr Johnson said the UK's "quarrel is with Putin's Kremlin". 
 
 "We think it overwhelmingly likely that it was his decision to direct the use of a nerve agent on the streets of the UK, on the streets of Europe, for the first time since the Second World War," he said. 
 
 'UK is not alone' 
 
 Russian ex-spy Sergei Skripal, 66, and his daughter Yulia Skripal, 33, remain critically ill in hospital, after they were found unconscious on a bench in the Wiltshire city on 4 March. 
 
 The UK government says they were poisoned with a nerve agent of a type developed by Russia called Novichok, and PM Theresa May said she believed Moscow was "culpable". 
 
 Image copyright EPA/ Yulia Skripal/Facebook Image caption Sergei Skripal, 66, and his daughter Yulia, 33, are in a critical condition in hospital 
 
 Mrs May has said the UK will expel 23 Russian diplomats as part of a "full and robust" response - prompting Russia's Foreign Minister Sergei Lavrov to say it will "certainly" expel British diplomats in response. 
 
 Russia's investigative committee said it had opened a criminal case investigation into the "attempted murder" of Ms Skripal and "the murder" of Nikolai Glushkov, a Russian exile who was found dead in his home in London on Monday. 
 
 According to Russian news agency Tass, the Russian ambassador to Britain, Alexander Yakovenko, said the UK claimed the nerve agent used was A-234, but this has not been confirmed. 
 
 A Downing Street spokesman said the Organisation for the Prohibition of Chemical Weapons (OPCW) has been invited to come to the UK to take a sample of the nerve agent - that process is expected to begin "imminently". 
 
 Analysis: Was chemical A-234 used? 
 
 By Gordon Corera, BBC security correspondent 
 
 The implication of the ambassador's comments is that the Russians have been told by the British the exact nerve agent deployed. 
 
 So far, British officials have not confirmed that they have communicated this to Moscow or that A-234 was the exact agent deployed. 
 
 Based on public sources, A-234 is one of the Novichok family of agents. 
 
 It has been reported that it is at least five to eight and possibly 10 times as strong as VX. 
 
 Little is known about it but the symptoms are very similar to those which eyewitnesses attributed to Sergei and Yulia Skripal. 
 
 In military handbooks it is described as a "delayed casualty agent" - its persistence depends upon how it is used, as well as the weather. 
 
 On Friday, Nato Secretary General Jens Stoltenberg said the alliance had "no reason to doubt the findings and assessments by the British government" which suggested Russian responsibility. 
 
 He said the "UK is not alone" and Nato allies gave "strong political support" to Britain, following a joint statement from the US, France and Germany backing Mrs May's government and a pledge of support from Australia. 
 
 Speaking to BBC Radio 4's Today programme, Mr Stoltenberg said the incident was part of a "pattern of reckless behaviour" from Russia, following allegations of cyber attacks and election meddling in recent years. 
 
 "It is important that Russia gets a clear signal that it costs to behave the way they behave," Mr Stoltenberg said. 
 
 Media playback is unsupported on your device Media caption The BBC's Gordon Corera considers how likely is it Russia poisoned Sergei Skripal and his daughter 
 
 "I'm absolutely certain that Russia has underestimated the resolve and unity of Nato allies when we have implemented different kinds of sanctions over the last years," Mr Stoltenberg added. 
 
 But Kremlin spokesman Dmitry Peskov said Russia was not worried by international expressions of support for the UK and challenged Britain to "provide some confirmation". 
 
 He said: "Sooner or later, the British will have to show some proof to those 'colleagues' who say they are with UK on this; sooner or later will have to stand up its accusations." 
 
 Ahead of an EU leaders' summit, German Chancellor Angela Merkel said discussions of a potential boycott of the World Cup in Russia are "not an immediate priority". 
 
 It comes as Labour leader Jeremy Corbyn has written in the Guardian warning against "hasty judgements", and not to "rush ahead of the evidence". 
 
 No symptoms 
 
 Wiltshire Police said 131 people had been identified as potentially being exposed to the nerve agent - but none has shown any symptoms. 
 
 Salisbury District Hospital has also assessed 46 people who came forward expressing health concerns but they were not admitted. 
 
 In a letter to the Times, Salisbury NHS Trust emergency medical consultant Stephen Davies said only three people - the Skripals and Det Sgt Nick Bailey - had needed treatment. 
 
 Det Sgt Bailey remains in a serious but stable condition in hospital after being contaminated with the chemical. 
 
 Public Health England said the risk posed to the public remains low but they repeated their advice for anyone who had been to the Mill pub or Zizzi to wash their clothes and possessions. 
 
 A spokesperson said while it was clear a "significant dose" could have a "serious immediate effect", anyone in either venue "could only have been exposed to extremely small traces" and no further cases of illness have been reported. 
 
 Russia's ambassador to Britain Alexander Yakovenko claimed the UK had angled allegations against Russia to "divert attention from Brexit". 
 
 He criticised the lack of transparency and said: "Nobody saw even the pictures of these people in a hospital, whether they are alive or maybe they are in good health. Nobody talked to the doctors." 
 
 And Russia's Foreign Minister Sergei Lavrov said Russia had asked the UK to take action under the Chemical Weapons Convention. 
 
 He also responded to Defence Secretary Gavin Williamson - who previously said Russia should "go away" and "shut up" - saying: "Maybe he lacks education." 
 
 Some 220 police officers from 16 forces, 80 ambulance staff, 50 fire officers, 200 armed forces personnel and 250 specialist officers have so far been deployed as part of the investigation, Wiltshire Police said. 
 
 Image copyright PA Image caption Police cordons remain in place in parts of Salisbury, 12 days on from the attack 
 
 Image copyright Getty Images Image caption Zizzi restaurant, the Mill pub and the bench where the Skripals sat are among locations taped off by police 
 
 On Thursday, Mrs May visited Salisbury to speak to emergency service workers, public health experts and local business owners who are affected by the police cordons. 
 
 Wiltshire Council has announced measures to help affected businesses, including free park and ride journeys and waived business rates. 
 
 Mr Skripal is a retired colonel in the Russian military intelligence service. 
 
 He was jailed by Moscow in 2006 for secretly working for Britain's MI6 but was later released and allowed to come to the UK. ||||| People walk passed the British Consulate General, in St.Petersburg, Russia, Saturday, March 17, 2018. Russia on Saturday announced it is expelling 23 British diplomats and threatened further measures... (Associated Press) 
 
 People walk passed the British Consulate General, in St.Petersburg, Russia, Saturday, March 17, 2018. Russia on Saturday announced it is expelling 23 British diplomats and threatened further measures in retaliation in a growing diplomatic dispute over a nerve agent attack on a former spy in Britain.... (Associated Press) 
 
 People walk passed the British Consulate General, in St.Petersburg, Russia, Saturday, March 17, 2018. Russia on Saturday announced it is expelling 23 British diplomats and threatened further measures in retaliation in a growing diplomatic dispute over a nerve agent attack on a former spy in Britain.... (Associated Press) People walk passed the British Consulate General, in St.Petersburg, Russia, Saturday, March 17, 2018. Russia on Saturday announced it is expelling 23 British diplomats and threatened further measures... (Associated Press) 
 
 LONDON (AP) — Britain's foreign secretary said Sunday that the trail of blame for the poisoning of a former spy "leads inexorably to the Kremlin," after a Russian envoy suggested the nerve agent involved could have come from a U.K. lab. 
 
 Foreign Secretary Boris Johnson said Britain has evidence that Russia has been stockpiling nerve agents like the one used against Sergei Skripal and his daughter Yulia. 
 
 Johnson told the BBC that officials from the Netherlands-based Organization for the Prohibition of Chemical Weapons would arrive in Britain on Monday to take samples of the nerve agent used to poison the Skripals. Britain says it is Novichok, a class of powerful nerve agent developed in the Soviet Union toward the end of the Cold War. 
 
 "We actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination but has also been creating and stockpiling Novichok," Johnson said. 
 
 Vladimir Chizhov, Moscow's EU ambassador, said Russia has no chemical weapons stockpiles and was not behind the poisoning. 
 
 "Russia had nothing to do with it," Chizhov told the BBC. 
 
 Chizhov pointed out that the U.K. chemical weapons research facility, Porton Down, is only eight miles (12 kilometers) from Salisbury, where Sergei Skripal —a former Russian intelligence officer convicted in his home country of spying for Britain— and his daughter were found March 4. They remain in critical condition. 
 
 Asked whether he was saying Porton Down was responsible, Chizhov replied: "I don't know." 
 
 The British government dismissed the ambassador's suggestion as "nonsense." 
 
 Johnson said it was "not the response of a country that really believed itself to be innocent." 
 
 Britain and Russia have each expelled 23 diplomats and taken other measures in the escalating tit-for-tat dispute. 
 
 Johnson said Britain's National Security Council will meet this week to discuss "what further measures if any" the country will take. 
 
 Opposition lawmakers are calling on the government to clamp down on the illicitly gained money of wealthy Russians in Britain. Critics say U.K. authorities have been slow to investigate the origins of the wealth invested in London's financial district and property market. 
 
 Russia's ambassador in London, Alexander Yakovenko, called for "cooler heads," telling the Mail on Sunday that the dispute is "escalating dangerously and out of proportion."
– Britain's foreign secretary said Sunday that the trail of blame for the poisoning of a former spy "leads inexorably to the Kremlin," reports the AP, after a Russian envoy suggested the nerve agent could have come from a UK lab. "We actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination but has also been creating and stockpiling Novichok," Foreign Secretary Boris Johnson tells the BBC. "We think it overwhelmingly likely that it was (Vladimir Putin's) decision to direct the use of a nerve agent ... on the streets of Europe for the first time since the Second World War." Johnson said officials from the Organization for the Prohibition of Chemical Weapons would arrive in Britain on Monday to take samples of the nerve agent used to poison Sergei Skripal and his daughter Yulia. Britain says it is Novichok, a powerful nerve agent developed in the Soviet Union at the end of the Cold War. Vladimir Chizhov, Moscow's EU ambassador, said Russia has no chemical weapons stockpiles and was not behind the poisoning. "Russia had nothing to do with it," Chizhov told the BBC. Chizhov pointed out that the UK chemical weapons research facility, Porton Down, is only eight miles from Salisbury, where the Skripals were found March 4. They remain in critical condition. Asked whether he was saying Porton Down was responsible, Chizhov replied: "I don't know." The British government dismissed the ambassador's suggestion as "nonsense." Johnson said it was "not the response of a country that really believed itself to be innocent." Russia's ambassador in London, Alexander Yakovenko, called for "cooler heads," telling the Mail on Sunday that the dispute is "escalating dangerously and out of proportion." Britain and Russia have each expelled 23 diplomats.