U.K. Prime Minister Theresa May faces calls to crack down on Russian influence in Britain amid reports that investigators have linked Vladimir Putin's regime to last week's poisoning of a former spy in a city southwest of London.

The Times and Telegraph newspapers reported that May could blame Russia publicly as early as Monday for the attempted nerve-gas murder of Sergei Skripal and his daughter Yulia. They remained in a hospital on Sunday, while May is drawing up plans to cancel the visas of Russians linked to Putin and impose sanctions, the papers said.

May and her senior security officials have been careful to avoid pointing the finger at Russia, saying they're waiting for the inquiry to report back first. The Times reported that investigators have found evidence to link the nerve agent used in the attack to Moscow.