The agency said the upgrade reflected improved VimpelCom's profile and enhanced profitability on the back of the growing mobile services market in Russia and the Commonwealth of Independent States, an alliance of ex-Soviet countries.
The rating is constrained by high competition and downward trends in the sector, along with Russia's administrative environment, which also affects the predictability and stability of the company's operations, the agency said.
VimpelCom is majority owned by Norway's Telenor (26.6% of shares) and Altimo, the telecoms arm of Russian financial major Alfa Group (32.9%).
VimpelCom is listed on the Russian Industrial Leaders Index (RUXX) - a composite economic index of 20 Russian companies with financial instruments (shares and depository receipts) placed on bourses, including the New York Stock Exchange, the London Stock Exchange, Nasdaq and AMEX.
