The US media outlet quoted sources said that the British police reached the conclusion after combing through hours of CCTV footage from UK airports and the Salibury region, the place where the incident took place.

The police have identified two people as suspects, who they say have never been involved in prior attacks.

Meanwhile, in a second Novichok poisoning, a couple fell ill earlier this month.

While the female, 44-year-old Dawn Sturgess, later died, her partner Charlie Rowley, 45, remains in hospital.

Police have launched a murder investigation, after stating that the second attack may not been deliberate.