British officials are consulting with allies over a possible response to Russia after officials confirmed on Wednesday a second case of poisonings on British soil with a nerve agent in Russia’s Novichok series.

In the new case, a couple—which multiple media outlets have identified as Charlie Rowley, 45, and Dawn Sturgess, 44—became ill and lost consciousness on Saturday in Amesbury, a town in Wiltshire, England. Their location was just a few miles away from where former Russian double agent Sergei Skripal and his adult daughter, Yulia, were poisoned in March with a Novichok agent. On Wednesday, Scotland Yard reported that a chemical analysis identified the same Novichok agent as the cause of the new poisonings.

Britain’s home secretary Sajid Javid on Thursday called on Moscow to explain “exactly what has gone on” and said that the country will be “consulting with our international partners and allies following these latest developments.”

In the UK House of Commons, Javid continued, saying:

We will stand up to the actions that threaten our security and the security of our partners. 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.

Russia has firmly denied any involvement in both cases. Vladimir Putin’s personal spokesperson told reporters Thursday that “of course, we’re concerned that these substances have been used repeatedly in Europe... However, on the other hand, we have no information about which substances were used or how they were used.”

Russian state media is casting doubt on the poisonings as well as dismissing any notions of their country’s involvement. Various outlets accused British government officials and journalists of “dragging old skeletons out of the closet” and suggested the poisonings were staged.

Lingering question

As Ars has reported previously, Britain and its NATO allies united to blame Russia for the March poisoning of the Skripals. Britain expelled 23 Russian diplomats over the matter, and 26 other countries followed suit. An intelligence report in April specifically traced the Novichok nerve agent used in that attack to a Russian military laboratory.

Novichok, meaning “newcomer,” is a series of chemical weapons developed by the Soviet Union in the height of the cold war. The nerve agents were designed to be undetectable, possibly relying on combinations of otherwise harmless or unsuspicious chemicals. This would allow the Soviet Union to get around the Chemical Weapons Convention, which prohibit the stockpiling of chemical weapons and precursors.

The Novichok nerve agents cause harm by crippling the action of cholinesterase, an enzyme involved in the normal and essential breakdown of some neurotransmitters. That breakdown allows nerves to return to a resting state after they’ve fired. Without it—or when a Novichok agent hampers the enzyme—nerves can be continuously activated. This can lead to muscle twitching, paralyzed breathing, convulsions, and death. The poisons are thought to be eight to 10 times as powerful as VX or sarin gas.

Witnesses told British media outlets that, before losing consciousness, Rowley and Sturgess were frothing at the mouth, hallucinating, and incoherent. They remain in critical condition in a local hospital. Similarly, the Skripals were found slumped on a bench in a catatonic state back in March. After being placed in induced comas, both eventually regained consciousness and continue to recover in an undisclosed location.

British officials determined that the Skripals were likely poisoned after a would-be assassin smeared the nerve agent on the front door handle of Mr. Skripal’s home. It’s unclear how or why Rowley and Sturgess came into contact with nerve agent, however. British officials reported that there was nothing in their backgrounds to tie them to Russia or suggest they were targeted. Investigators are looking into whether they simply accidentally came across remnants of the batch of poison used in the Skripal attack. Thus, they may have been inadvertent victims from discarded or lingering nerve agent—a possibility likely to put residents on edge.

Russian chemist Vil Mirzayanov, who now lives in the US and first exposed the Novichok program, told the BBC that such as explanation is unlikely. He said the nerve agent is unstable, particularly in damp conditions, and would have decomposed in the four months since the Skripal attack. Instead, he suggested that the couple were victims of a fresh incident. Other chemical-weapons experts have described the poison as "relatively stable," however, and speculated that certain storage conditions could extend its life. For instance, the nerve agent could have resisted decay if it was suspended in a water-repelling gel, one expert suggested to The New York Times.

Meanwhile, British officials, who are still investigating both poisonings, say that the risk to the public is low. However, they have cordoned off several areas and advised locals to wash their clothes and wipe down their belongings if they were in those suspect areas.

This post has been updated.