Bermuda-based OneBeacon Insurance Group Ltd. estimates that its first-quarter combined ratio will be 112 percent, including approximately $44 million, or 10 points, of mainly US-based pretax catastrophe losses.

Combined ratio indicates the percentage of premium dollars spent on claims and expenses and a figure higher than 100 reflects an underwriting loss.

The property and casualty insurer's losses were primarily linked to March Northeast US storms. Of the estimated $44 million of current accident year catastrophe losses, about $10 million were incurred in its ongoing specialty lines business, the firm said.

In 2009, the company's first quarter combined ratio was 94 percent, or 18 points better than the projection announced yesterday.

OneBeacon estimated that its first-quarter specialty lines GAAP combined ratio will be 97 percent, including four points of catastrophe losses.

It said that the majority of the catastrophe losses were incurred in businesses the company was exiting, including $21 million in non-specialty commercial lines run-off business and $13 million in traditional personal lines, which it agreed to sell in February.

The sale of the personal lines business is expected to close before June 30. In December 2009, the company sold its non-specialty commercial lines business in a renewal rights transaction.

OneBeacon will release its first-quarter results on April 29.