LONDON (MarketWatch) -- Moody's Investor Service downgraded Washington Mutual Inc.'s WM, -0.55% credit rating to below investment grade late Thursday, citing WaMu's reduced financial flexibility, deteriorating asset quality and expected franchise erosion. The rating agency cut the group's senior unsecured rating to below investment grade at Ba2 from Baa3. It also reduced the long-term deposit and issuer ratings of the banking unit to Baa3 from Baa2, though this rating remains investment grade. Moody's added the outlook for the ratings is negative. In a response, Washington Mutual said it believes the decision to cut its ratings to below investment grade "is inconsistent with the company's current financial position." The firm added Moody's action appears to reflect the uncertainty in the market, rather than a thorough evaluation of its business.