The victims of the nerve agent emergency in Wiltshire were not directly targeted, the security minister has said.
Ben Wallace disclosed that the "working assumption" is that the pair were exposed to Novichok either as a result of the attack on former Russian spy Sergei Skripal and his daughter in Salisbury earlier this year, or "something else".
A man and woman, named locally as Dawn Sturgess and Charlie Rowley, were taken ill on Saturday in Amesbury, around eight miles from where the Skripals were poisoned in March.
Referring to the Salisbury incident, Mr Wallace told BBC Radio 4's Today programme: "I think what we said at the time was that this was a brazen and reckless attack in the heart of a very peaceful part of the United Kingdom, and that is part of the anger I feel about the Russian state is that they chose to use clearly a very, very toxic, highly dangerous weapon."
As the latest incident threatened to plunge Britain's relations with the Kremlin further into the deep freeze:
- It was understood investigators are working on a theory that the pair came into contact with the deadly substance in a part of Salisbury city centre that was outside the clean-up launched after the attack against the Skripals.
- There were warnings that the new Novichok poisoning will raise "serious questions" over the massive clean-up operation launched following the March incident.
- The man and woman remained critically ill in hospital.
- Public Health England (PHE) said it did not believe there to be a "significant health risk" to the wider public, although its advice was being reviewed.
- Home Secretary Sajid Javid was preparing to chair a meeting of the Cobra emergency committee on Thursday.
Officers were called to a home in Muggleton Road, Amesbury, on Saturday morning when the 44-year-old woman collapsed.
They were called back later that day when the man, 45, also fell ill.
It was initially believed that the two patients fell ill after possibly using drugs from a contaminated batch, police have said.
But after further tests, authorities declared a major incident and on Wednesday night counter-terror police assumed responsibility for the investigation after the Government's Porton Down laboratory concluded that the pair had been exposed to Novichok.
A senior Government source told the Press Association it is believed there was cross-contamination of the same batch of nerve agent involved in the "reckless" Salisbury attack, as opposed to a secondary attack.
"They (the authorities) have never been able to ascertain the item used to deposit the Novichok and it's possible the pair have come into contact with that item," the source said.
Metropolitan Police Assistant Commissioner Neil Basu, the country's most senior anti-terror officer, acknowledged there will be "a great deal of speculation" over potential links between the two incidents.
He said: "I would add that the complex investigation into the attempted murders of Yulia and Sergei remains ongoing and detectives continue to sift through and assess all the available evidence and are following every possible lead to identify those responsible, for what remains a reckless and barbaric criminal act.
"I must say that we are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to.
"The possibility that these two investigations might be linked is clearly a line of inquiry for us."
Health officials say their current advice, based on the small number of casualties affected, is that the risk to the public is low.
Professor Paul Cosford, medical director of Public Health England, told the Today programme: "The sites that were the subject of the clean-up after Skripal are not associated with this incident.
"So there should not be any concern that the clean-up after the previous incident has not worked here."
According to friend Sam Hobson, he visited the park with the couple on Friday evening.
He told The Guardian that, after Ms Sturgess was taken to hospital on Saturday morning, he accompanied Mr Rowley to a Boots chemist in Amesbury before the pair attended a free hog roast at a local baptist church.
The address where the couple were found is on a new housing development on the southern edge of the town, which lies close to Stonehenge.
Neighbours living near the scene were keen to find out more about what had happened to the couple.
College student Chloe Edwards, 17, described seeing police cars, fire engines and people in "green suits" on Saturday night.
"We were just eating our dinner and all these emergency vehicles turned up," she said.
"They were putting on these green suits and we thought it was the gas as our electricity was turned off as well."
She said the vehicles arrived at about 7pm and she and her family were told to stay inside their home until about 10pm.
"We wanted to know what happened and, with the Russian attack happening not long ago ... we just assumed the worst," she said.
The episode in Salisbury - the first use of a nerve agent in Europe since the Second World War - sparked international outrage.
The Kremlin has repeatedly denied being behind the attack.
Mr Skripal and his daughter Yulia have since left hospital.