The Guardian reports that Britain wants Russia to extradite two men over the Skripal nerve-agent case.
But it says that an extradition request is expected to be rejected by Russia.
Russians Sergei Skripal, a former double agent, and his daughter Yulia, were attacked with Novichok nerve agent in March. They were found unconscious on a public bench in Salisbury.
Citing government and security sources, the Guardian said that prosecutors had completed the extradition request for the suspects and it was ready to be submitted.
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The Russian Embassy said it had not received an official request. Russia denies any involvement in the attack.
Russian officials refused to hand over suspects in the murder case of Alexander Litvinenko. The Russian constitution prevents the extradition of Russian citizens to another state.
The Guardian says British investigators have pieced together the movements of two Russians in the Skripal attack.
Dawn Sturgess subsequently died from Novichok near Salisbury. Her partner, Charlie Rowley, was also stricken.