MOSCOW, Dec. 7 (Xinhua) -- The Russian Prosecutor General's office investigating the poisoning death of former spy Alexander Litvinenko said on Thursday in a statement that a Russian businessman was also found to have developed an illness connected with a radioactive nuclide.

    "The examinations revealed that Litvinenko died as a result of poisoning by a radioactive nuclide, and (Dmitry) Kovtun, who met with Litvinenko in London in October 2006, was diagnosed with a disease also connected with a radioactive nuclide," the statement said.

    Kovtun is the business partner of Andrei Lugovoi, who is also undergoing medical tests at a hospital in Moscow.

    Russian prosecutors on Thursday formally opened a criminal investigation into Litvinenko's death. The former spy died in London on Nov. 23.

    Kovtun and Lugovoi and another Russian businessman said they had met Litvinenko briefly at a hotel bar before attending a soccer match in a stadium in London.

    Traces of polonium-210, the isotope that killed Litvinenko, had been found at two spots in the stadium, the British health authority said.