"NTT's global expansion plans are within expectations," Moody's analyst Takahiro Morita told Reuters in an interview. He stressed, however, that the fast pace of change in Japan's telecoms sector, the world's second-largest, required constant vigilance.

"We are closely watching changing market conditions and their impact on NTT," Morita said, adding that for the time being, NTT's Aa1 rating - one notch below the top-grade triple-A - was stable.

Morita said the rating, downgraded last September due to increased competition in the domestic market, fully reflected a recent accord between Japan and the United States to cut NTT's interconnection charges, which competitors must pay for "last mile" local connections to users.