Britain demanded Thursday that Russia explain the poisoning of a couple who were exposed to the same nerve agent that hospitalised a former Russian spy and his daughter in an attempted murder blamed on Moscow.
British nationals Charlie Rowley, 45, and Dawn Sturgess, 44, are in critical condition in hospital after being found unconscious on Saturday at a house in Amesbury, Wiltshire.
They fell ill just 16 kilometres from the site where Sergei Skripal and his daughter Yulia were poisoned with Novichok, a military-grade nerve agent developed by the Soviet Union during the Cold War, in March.
That case sparked a major diplomatic row between London and Moscow. Britain and its allies pointed the finger at Russia, but the Kremlin denied any involvement. The latest poisoning threatens to widen the spat sparked by the initial case, which drew significant international condemnation of Russia.
British Home Secretary Sajid Javid said any link between the two cases was the “main line of inquiry”. He called Russia “barbaric and reckless”, appearing to suggest Moscow could have played a role in both incidents.
"We don't want to jump to conclusions but if it is established that the Russian state is entirely responsible for this as well, then of course we will be considering what further action we can take," Mr Javid told parliament on Thursday.
Mr Javid said the "strong working assumption" was that the pair had come into contact with the agent at a different location to the sites involving in the clean-up operation following the Skripal attack and had not been deliberately targeted.
In a warning to the Kremlin, he noted that the March poisoning had prompted international condemnation, with a number of Britain's allies expelling Russian diplomats from consulates and embassies.
“We will stand up to the actions that threaten our security and the security of our partners," Mr Javid said. "It is unacceptable for our people to be either deliberate or accidental targets, or for our streets, our parks, our towns to be dumping grounds for poison.”
Moscow issued a swift response to Mr Javid's comments as simmering tensions over the Skripal attack were reignited on Thursday afternoon, saying that the British government was subjecting Russia to "hell".
Russia's presidential spokesman Dmitry Peskov said the country had no involvement in the second poisoning, adding that Britain had failed to produce any convincing evidence for either incident.
"We do not have information about what substances were used and how they were used," Mr Peskov said, describing the case as "very worrying".
The Russian Foreign Ministry warned Britain's police force, which has launched a full scale counter terror operation, not to get involved in political game playing.
"We urge British law enforcement not to get involved in dirty political games that certain powers in London have already begun and instead finally cooperate with Russian law enforcement in their investigations," Russian foreign ministry spokeswoman Maria Zakharova told a briefing.
Earlier on Thursday, British Security Minister Ben Wallace appealed to Russia to give details about its alleged involvement in the nerve agent attack on the Skripals in order to protect the public.
"The Russian state could put this 'wrong' right, they could tell us what happened, what they did and fill in some of the significant gaps that we are trying to pursue," Mr Wallace told BBC radio.
"They are the ones who could fill in all the clues to keep people safe."
Mr Skripal, 66, and his 33-year-old daughter were left fighting for their lives after being exposed to Novichok four months ago but have since been discharged from hospital. Police said they believe the agent was smeared on the front door of Mr Skripal’s house in Salisbury.
Police initially believed the latest victims had taken heroin or crack cocaine from a contaminated batch of drugs when emergency services were called to their property on Muggleton Road, Amesbury at the weekend.
Mr Javid said scientists at Britain’s military research laboratory Porton Down had since established "this is the exact same nerve agent from the Novichok family" as the one used in the March attack.
"We cannot attribute this to the same batch at this point," he added, but said researchers at the facility would continue to investigate.
Meanwhile, 100 counter terror officers have joined Wiltshire police to establish whether the Amesbury pair were poisoned by Novichok dumped by the Skripal's attackers.
The second case of Novichok poisoning comes as Russia hosts the World Cup, a month-long global festival of football in which both England and Russia remain at the quarter-final stage.
Russian politicians, diplomats and media outlets mocked Britain for suggesting that it would have carried out a poisoning in the middle of hosting one of the world’s biggest sporting occasions.
"How dumb (do) they think (Russia) is to use 'again' so-called 'Novichok' in the middle of the FIFA World Cup...The show must go on?," Russia's embassy to the Netherlands wrote on Twitter on Thursday.
Sputnik News, a Russian state news site, said if England reached the World Cup final, it would leave British Prime Minister Theresa May with a “political dilemma,” jibing her over the British government’s boycott of the tournament in reaction to the Skripal case.
Sergei Zheleznyak, deputy speaker of the State Duma, Russia's lower house of parliament, told state TV that the new case looked like an attempt to change England soccer fans' positive perception of Russia.
Britain’s emergency committee Cobra met on Thursday chaired by Mr Javid, while Mrs May travelled to Germany to meet Chancellor Angela Merkel.
Speaking in Berlin, Mrs May described the latest incident as “obviously deeply disturbing” after another poisoning on British soil.
“The police I know will be leaving no stone unturned in their investigation,” she added.
Several sites that investigators believe the couple frequented before they fell ill remained cordoned off on Thursday. These include a chemist and a church in Amesbury as well as a park in Salisbury.
Health officials said the risk to the public remained low but said anyone experiencing symptoms should seek medical advice urgently.