Relations between the United Kingdom and Russian Federation are at the worst they have been since the end of the Cold War after the nerve agent attack on Sergei Skripal, a former spy, and his daughter Yulia.
Britain's Press Association news agency reported last month that police had identified two Russian suspects in the Salisbury attack on former Russian spy Sergei Skripal and his daughter, Yulia, but there has been no official confirmation of that report either.
The Guardian says British investigators have pieced together the movements of two Russians in the Skripal attack.
They were both found unconscious on a bench in a shopping centre after being exposed to novichok - they were initially thought to have been intoxicated.
Putin rejected a similar extradition request in 2007 for two Russians suspected of being behind the 2006 assassination with polonium of the former FSB officer Alexander Litvinenko in London.
The Crown Prosecution Service (CPS), which has been preparing papers, has completed the process and is ready to file, the Guardian reported on Monday.
Russian Federation has previously rejected similar extradition requests.
The government has been consistent in pointing the finger of blame at Moscow for the poisoning using Novichok - a military-grade nerve agent developed by the former Soviet Union. Later, Sturgess died in the hospital, the other victims were discharged after treatment. Moscow refused to extradite Russians in accordance with the Constitution.
Mr Rowley, like the Skripals, recovered from the attack but Ms Sturgess, his partner, died.
Police have said they believe the two incidents are related, theorizing that perpetrators first smeared the Novichok on the door of Sergei Skripal's house and discarded the container, which Rowley later picked up and gave to Sturgess, who sprayed it on her wrists.
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