MOSCOW, September 21 (RIA Novosti) - Standard & Poor's has upgraded the long-term credit rating of Russia's third largest mobile firm MegaFon to BBB- from BB+ with a stable outlook, the international rating agency said on Monday.

The company's national scale long-term rating was also raised to ruAAA from ruAA+ with stable outlook, S&P said.

The ratings were upgraded as the company stably demonstrated high financial performance, including high creditworthiness indices, providing flexibility for the mobile firm to finance moderate organic growth, acquire assets and make payments to shareholders, S&P said in a statement.

MegaFon announced early in September that its U.S. GAAP net profit grew 4% year-on-year in January-June 2009 to 20.1 billion rubles ($638 million).

MegaFon, which was established in 2002, said its revenues in the reporting period increased 7.3% to 86.1 billion rubles ($2.7 billion), and earnings before interest, taxes, depreciation and amortization (EBITDA) rose 5.3% to 41.58 billion rubles ($1.3 billion).

"By the end of the current period we managed to reverse the negative trends which were evident at the beginning of this year," MegaFon said in a statement.

MegaFon had 45.8 million registered subscribers in Russia at the end of June 2009.