Britain's interior minister accused Russia on Thursday of turning the U.K. into a "dumping grounds for poison," and demanded an explanation on how two people were inadvertently poisoned with the same military-grade nerve agent used to attack a former Russian spy and his daughter in the same area four months ago.
A man and woman in their 40s were in critical condition Thursday at a hospital in southwest England after they fell ill Saturday near Salisbury, a city not far from Britain's iconic Stonehenge monument.
Experts at Britain's Porton Down chemical weapons laboratory have determined that the two were exposed to the same type of Novichok nerve agent that was used to attack ex-spy Sergei Skripal and his daughter, Yulia, on March 4 in Salisbury.
Britain has accused Russia of being behind the Skripal attack but the Kremlin denies any involvement. British Home Secretary Sajid Javid told Parliament on Thursday that it is now time for Russia to explain "exactly what has gone on."
"It is completely 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," Javid said.
The unexplained poisoning of two British citizens with no apparent link to Russia raised health concerns in Salisbury, where a massive decontamination effort took place after the Skripal poisoning case.
There was no panic as police cordons sprang up again and police stood guard near potential contamination sites Thursday. Still, residents could not contain their unease with a second brush with Novichok, even though public health officials said the risk of contamination to anyone was very low.
Keith Burton, 56, was among the concerned.
"We had hoped it was all over and done with," he said. "Perhaps they forgot about something? Perhaps it was something dropped somewhere? We simply don't know."
Experts say just a few milligrams of the odorless liquid — the weight of a snowflake — is enough to kill a person within minutes. Finding it is the problem.
British officials say they believe the nerve agent was smeared on Skripal's door, but have not explained how that was done. They had a timeline of the Skripals' movements in Salisbury as they became ill, and spent millions of pounds cleaning those known sites. But they have not explained how they can, or cannot, track the nerve agent through an area.
Chemical weapons expert Hamish de Bretton-Gordon said the latest victims are likely collateral damage from the Skripal attack.
"The Novichok gel that was smeared on the handle of the Skripals' house was presumably transported in some device or syringe," he said. "I think the working assumption now is that device or that syringe is what has appeared and the residue caused these two people to become ill."
The new case has surfaced days before a NATO summit that is expected to address the worsening relations between Russia and the West. It also comes as Russia hosts the World Cup — a monthlong global extravaganza in which both the English and Russian soccer teams have advanced so far.
The Kremlin's spokesman says Russia is concerned about the case but had nothing to do with either poisoning.
"Russia has categorically denied and continues to categorically deny the possibility of any kind of involvement to what was happening there," President Vladimir Putin's spokesman, Dmitry Peskov, told reporters Thursday.
Peskov noted that Britain rejected Russia's offer of a joint probe of the Skripal case, adding that the U.K. "has not presented any evidence of Russia's involvement in this, besides unfounded accusations."
Britain has said the type of nerve agent used in the Skripal attack was developed by the Soviet Union and could only have been produced by a state agency. British Prime Minister Theresa May gave Russia a deadline to explain how Novichok could have been used in Britain, and when the Kremlin failed to respond the government said it had no option but to believe the Russian state was involved in the attack.
Javid said Thursday the nerve agent involved in the current case was the same variety as that used against Skripal and his daughter, but it's not clear whether the two samples came from the same batch.
"What we are clear on ... is that this is the exact same nerve agent from the Novichok family," he said. "We cannot attribute this to the same batch at this point. Scientists will be looking into that. I am also told that may not even be possible."
Local police declared the recent poisoning a "major incident" Wednesday, four days after the couple — identified by friends as 44-year-old Dawn Sturgess and 45-year-old Charlie Rowley — were found at a residential building in Amesbury, eight miles (13 kilometers) from Salisbury.
Authorities initially thought the two had taken a contaminated batch of heroin or crack cocaine.
Police cordoned off a home in Amesbury, believed to be Rowley's, and other places the pair visited, including a church, a pharmacy and a park in Salisbury near where the Skripals were found.
The Skripals' illness initially baffled doctors after they were found unconscious on a park bench in Salisbury in March. Scientists at the Porton Down concluded they had been poisoned with Novichok.
Andrea Sella, professor of inorganic chemistry at University College London, said Novichok nerve agents "are designed to be quite persistent — they hang around in the environment, neither evaporating or decomposing quickly.
"That means that if a container or a surface was contaminated with this material, it would remain a danger for a long time. And it will be vital to trace the movements of this couple to identify where they might have come into contact with the source," he said. "So while the public at large are at very low risk from this material, until the source is found there is a remote chance that someone else might come into contact with it."
Ben Wallace, Britain's security minister, said the Russians should come forward and tell British authorities what they know about the Novichok poisonings.
"I'm waiting for the phone call from the Russian state," he said. "The offer is there. They are the ones who could fill in all the clues to keep people safe."
Matt Dunham and Vladimir Isachenkov contributed to this report.
CORRECTION (Thursday, July 5, 2018, 5:40 a.m. ET): An earlier version of this story misspelled the first name of police official Neil Basu.