MOSCOW, April 7 (RIA Novosti) - Fitch Ratings said on Monday it had assigned Russia's largest mobile phone operator Mobile TeleSystems (MTS) a long-term issuer default rating of BB+ with a stable outlook.

The agency gave the company a national long-term rating of AA+(rus) and a short-term issuer default rating of B.

"MTS is a highly profitable and operationally successful mobile operator in the CIS region that achieved a relatively mature stage in its business cycle as evidenced by its positive free cash flow generation," said Nikolay Lukashevich, senior director of Fitch's telecommunications, media and technology team.

"However, the company is not immune to the group-wide risks of JSFC Sistema, its controlling shareholder, which is a credit constraint," he said.

The company's revenue in 2007 exceeded 8 billion.