LONDON — The British government on Thursday called on Russia to explain ‘‘exactly what has gone on’’ after a British couple fell into a coma following exposure to the same type of Soviet-era nerve agent used in March to poison a former spy and his daughter.
The latest health crisis involving the chemical Novichok came about eight miles from the site where former Russian double agent Sergei Skripal and his adult daughter, Yulia, were stricken four months ago.
The couple was exposed to the nerve agent after ‘‘handling a contaminated item,’’ the Metropolitan Police said in a statement.
Investigators are trying to determine if this was residual contamination from the March attack, which British authorities linked to the Russian government. Moscow has categorically denied any involvement.
If remnants of the March attack are proven, it could raise wider concerns that health officials failed to eliminate exposure risks after an extensive cleanup. But another, more troubling scenario would be that it was a different batch of Novichok that sickened the British couple on Saturday in the small town of Amesbury.
‘‘It is now time that the Russian state comes forward and explains exactly what has gone on,’’ Sajid Javid, Britain’s home secretary, told Parliament.
Witnesses told the British press that the couple — identified as Charlie Rowley, 45, and Dawn Sturgess, 44 — were frothing at the mouth and incoherent before lapsing into coma. They were in critical condition at Salisbury District hospital, the same hospital where the Skripals were treated.
‘‘It is completely unacceptable for our people to be either deliberate or accidental targets,’’ Javid told Parliament, adding that it was also unacceptable for British streets or parks to be ‘‘dumping grounds for poison.’’
Russia hit back, urging Britain to avoid meddling.
Maria Zakharova, Russia’s Foreign Ministry spokeswoman, told reporters in Moscow that Britain should avoid ‘‘dirty political games’’ and should instead cooperate with Russian law enforcement.
The Russian Embassy in London called for a joint investigation into the Salisbury incident.
The episode threatens to further sour British-Russian relations, which were already in a deep freeze following the attempted murder of the Skripals.
Britain condemned that attack and expelled 23 Russian diplomats. At least 26 other countries joined in retaliatory measures, also expelling Russian diplomats. British ministers and members of the royal family have also boycotted the World Cup in Russia.
‘‘I know that many of you will question whether this incident is linked to that one,’’ Javid said, referring to the Skripal poisoning. ‘‘That is clearly the main line of inquiry. However, we must not jump to conclusions, and we must give the police the space and the time to carry out their investigations.’’
Officials have insisted the risk to the public is low. They say the current theory is that the British pair came into contact with nerve agent at a location not covered in Skripal decontamination sites.
Health officials have advised as a ‘‘highly precautionary measure’’ that those who visited the sites Rowley and Sturgess went to on Friday and Saturday wash their clothes and wipe down their belongings. They also urged locals not to pick up any unknown items.
Britain’s security minister, Ben Wallace, told the BBC the ‘‘working assumption’’ is that the British pair were not targeted, and he called on Russia to help by passing along details of the original attack.
‘‘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 . . . They can come and tell us what happened. I’m waiting for the phone call from the Russian state.’’
Experts also wonder if the latest victims came into contact with remnants of Novichok from the original attack.
‘‘It’s not looking like a new attack,’’ said Hamish De Bretton-Gordon, a former commanding officer of the British Army’s chemical and biological weapons unit. He is not involved in the current investigation, but said that ‘‘from what I understand, this is debris or collateral from the original attack, possibly contained in a syringe or medical container.’’
He said the assailant could have discarded the residue Novichok four months ago in the park in Salisbury, or in the nearby river, which is currently low.
‘‘Why the couple then picked it up and became infected, we don’t know. Probably just very bad luck,’’ he said.