NEW YORK (AP) - Fitch Ratings placed the BBB+ issuer default ratings of Bermuda-based White Mountains Insurance Group Ltd. on ratings watch negative.

The move also applies to the BBB+ issuer default ratings of its wholly owned intermediate holding company, White Mountains Re Group Ltd. and its majority owned intermediate holding company, OneBeacon US Holdings Inc.

In addition, Fitch placed on rating watch negative the "BBB" senior debt ratings of White Mountains Re and OB Holdings.

The ratings are all considered investment grade.

Fitch affirmed the insurer financial strength ratings for OneBeacon Insurance Group at A, for White Mountains Re's reinsurance subsidiaries White Mountains Reinsurance Company of America and Sirius International Insurance Corporation at A-, and for White Mountains Re Bermuda Ltd. at A. The rating outlook on all insurer financial strength ratings was revised to negative from stable.

Fitch said the revisions reflects its view the company faces increased risk due to its dramatic loss of shareholder equity, which stood at $2.9 billion on December 31, down 38 percent for the year. The stock closed on December 31 at $267.11, and ended Monday's session at $165.40, a drop of more than 38 percent since the start of the year.

The sharp stock decline increased debt-to-total capital ratio to 28 percent at year-end 2008 from 21 percent on December 31, 2007.