March 24 (Bloomberg) -- OAO GMK Norilsk Nickel, Russia’s biggest mining company, fell the most in a month after a report that Deputy Prime Minister Igor Sechin is inquiring about the company’s finances.

Sechin sent a letter demanding an explanation of Norilsk’s spending 86 billion rubles ($2.6 billion) on a share buyback, giving up control of its pension fund and selling mining licenses to a company owned by former Chief Executive Officer Mikhail Prokhorov, the Vedomosti newspaper said, citing two unidentified people close to the company.

“News of such a broad range of government investigation is likely to put strong pressure on the stock,” UniCredit SpA analysts Marat Gabitov and George Buzhenitsa said in a note.

Norilsk shares plunged as much as 10 percent to 2,233.30 rubles as of 11 a.m. in Moscow, falling from a four-month high. Erzhena Mintasova, a spokeswoman for Norilsk, couldn’t immediately be reached for comment on her mobile phone.

To contact the reporter on this story: William Mauldin in Moscow at wmauldin1@bloomberg.net

Last Updated: March 24, 2009 04:11 EDT