Russia has highlighted what it considers are two inconsistencies in the UK’s claim that Moscow was behind Novichok poisonings on English soil.
Britain’s prime minister, Theresa May, told parliament this week that two Russian intelligence officers were behind the attacks on double agent Sergei Skripal and his daughter, Yulia, in Salisbury, southern England.
But Vassily Nebenzia, Russia’s ambassador to the UN, hit back at May’s claims, calling them lies and pointing to two alleged discrepancies in the evidence.
Here we look at Moscow's claims in a more detail.
Claim 1: The photos of the suspects
Police released CCTV footage of suspects Alexander Petrov and Ruslan Boshirov arriving at Gatwick Airport, south of London, in the days before the attack on the Skripals.
In the corner of both images there is a time stamp from the surveillance equipment. Both show identical text: “02/03/2018 16:22:43”
Nebenzia said in a statement: “The number of 'inconsistencies' and open questions in connection with the new British 'evidence' is off the scale. For example, on the photos of suspects from London, on which they are captured passing through an identical corridor, allegedly at Gatwick airport, the time coincides with the accuracy of a fraction of a second.”
Russia is essentially arguing the photos are fake because you cannot have two people in a single corridor at exactly the same time.
But a social media user has countered that specialist multi-lane gates at Gatwick would potentially allow two people to be captured on film at the same time.
Claim 2: The perfume bottle
British police have linked the poisoning of the Skripals with a case nearly four months later that saw Charlie Rowley and his partner, Dawn Sturgess, hospitalised after they came into contact with the same military-grade nerve agent.
Rowley later said he had found what he thought was a perfume bottle and gave it to Sturgess as a gift.
The bottle contained Novichok and Sturgess later died in hospital.
Nebenzia has argued if the British are saying Petrov and Boshirov brought Novichok into the country in this Nina Ricci bottle then there is a key inconsistency.
He says the substance is so toxic it would have meant the two suspects would have been poisoned as well.
But police in the UK claim the container is not a genuine perfume bottle; they say it was a counterfeit box and the nozzle had been specially-adapted.
“We have spoken to Nina Ricci and undertaken further inquiries,” said the Metropolitan Police in a statement.
“Nina Ricci and our enquiries have confirmed that it is not a genuine Nina Ricci perfume bottle, box or nozzle.
“It is in fact a counterfeit box, bottle and nozzle that have been especially adapted.”