SoftBank Group issued a sharp rebuke Tuesday after S&P Global Ratings cut its long-term credit rating a notch further into junk territory, citing the Japanese technology conglomerate’s exposure to private market valuations and other external risk factors.

S&P said SoftBank’s credit risks are rising because it’s selling off public assets, such as Alibaba Group Holding, and increasing its exposure to private startups with more volatile valuations as a result. It downgraded the company’s rating to BB from BB+.

SoftBank shares fell as much as 2.3% in Tokyo, while its credit default swaps — the cost to insure SoftBank’s debt — rose by the most in about a month.