Moody's Investors Service Tuesday lowered its ratings on the long-term debt of J.P. Morgan & Co., citing concern over the bank's strategic repositioning toward investment banking.

"Though diversified, the company's businesses are increasingly sensitive to the behavior of global financial markets and resulting capital markets transaction levels," the rating agency said.

Moody's lowered Morgan's senior debt to Aa2 from Aa1 (senior), and confirmed its Prime-1 rating of commercial paper. The move affected about $5.4 billion of securities.

The bank disagreed with the rating change, saying that it "continues to merit the highest ratings."

"By traditional measures of creditworthiness - capitalization, asset quality, and long term profitability - Morgan remains an exceptionally sound institution," the bank said.

The other major rating agency, Standard & Poor's Corp., last year placed a negative outlook on the debt of Morgan, which is the only bank to carry a triple A rating - for its senior unsecured debt.

S&P, while maintaining its ratings, has raised concerns about the volatility of Morgan's trading income.

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