Police believe they have identified the suspected perpetrators of the novichok attack on former Russian double agent Sergei Skripal, the Press Association has reported.
But security minister Ben Wallace dismissed the report as "wild speculation" on Twitter.
The 66-year-old and his 33-year-old daughter Yulia were attacked with the deadly nerve agent at their home in Salisbury, Wiltshire.
The pair were taken to hospital after shoppers found them collapsed on a bench at The Maltings shopping centre on 4 March.
Both survived the attack and were discharged from Salisbury District Hospital after extensive treatment.
Officers believe several Russians were involved in the attempted murder and say they are looking for more than one suspect.
"Investigators believe they have identified the suspected perpetrators of the novichok attack through CCTV and have cross-checked this with records of people who entered the country around that time," a source close to the investigation told PA.
They said investigators were "sure" the suspects were Russian.
Scotland Yard, which is leading the investigation, declined to comment.
Sky's crime correspondent Martin Brunt said: "This would chime with the government's long-held belief that the Russian state was behind the attack on the Skripals, or at least had lost control of the nerve agent novichok which scientists say is made only in Russia."
In an analysis of samples taken from the Skripals' home, the highest concentrations of the toxic chemical was found on door handles.
The day before the pair were found unconscious by members of the public in Salisbury town centre, Mr Skripal was driven to Heathrow Airport by a friend to collect his daughter returning from the Russian capital, Moscow.
Brunt said this left around a five-hour window for the attackers to visit their home to apply the nerve agent.
He said police officers had collected 5,000 hours of CCTV from the local area during the course of their enquiries.
"Those images would have been matched with CCTV taken from Heathrow Airport and any other airport within a few days of the attack," said Brunt.
"That gives you an insight into the kind of meticulous and complex work that has been going on.
"It may be that through that work police have come to the conclusion that they have found people who were around the Skripals' home on 3 or 4 March and have been able to identify similar figures, or the same figures, getting on flights and perhaps going back to Russia."
The breakthrough comes as an inquest was opened into the death of Dawn Sturgess.
She and her partner Charlie Rowley, both from Amesbury which is situated about eight miles north of Salisbury, were poisoned by novichok believed to be from the same batch as that used to target the Skripals.
Ms Sturgess, 44, died earlier this month - eight days after being exposed to 10 times the amount of nerve agent the former spy and his daughter came into contact with.
Investigators believe the substance was in a discarded perfume bottle that the couple found in a park and that Ms Sturgess likely sprayed the substance directly onto her skin.
Mr Rowley, 45, survived coming into contact with the chemical and is still being treated in hospital.
David Ridley, senior coroner for Wiltshire and Swindon, confirmed a small glass bottle of fluid was recovered by investigators and that tests showed it contained novichok.
He said details of the cause of Ms Sturgess's death would not be disclosed until further tests had been carried out and adjourned the inquest until 16 January, 2019.
More than 400 exhibits, samples and items have been recovered by police investigating the poisoning of the couple.
A high police presence remains in Amesbury and Salisbury as searches of properties and a clean-up of public places continues.
Public Health England has said the risk to the public remains low, but has advised people not to pick up any unknown items such as syringes, needles, cosmetics, or similar objects made of materials such as metal, plastic or glass.
"The advice remains, 'if you didn't drop it, then don't pick it up'," it said.
The government has continued to make clear it believes the Russian state was behind the attack on the Skripals.
Vladimir Putin and other senior Russian politicians have continued to deny any involvement in the poisonings.
The row has led to tit-for-tat diplomatic expulsions between the UK, its allies and Russia.