Standard & Poor's Corp. on Thursday yanked Union Bank of Switzerland's AAA rating.

The rating agency affirmed its short-term ratings on the Swiss bank's debt but cut its long-term rating to AA-plus. That left Rabobank NV of Utrecht in the Netherlands and J.P. Morgan & Co.'s New York unit, Morgan Guaranty Trust Co., as the only major banks in S&P's top rating category.

Some smaller, government-owned banking units have AAA ratings.

S&P said the downrating reflected continued asset-quality problems in Union Bank of Switzerland's home market.

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