Wind and hail losses more than offset improved investment results for Liberty Mutual in the first quarter, driving net profit down 11% to $US351 million ($469 million).

The combined operating ratio deteriorated 5.2 points to 101.5%, the US-based company says.

Net written premium grew 5.3% to $US9.23 billion ($12.3 billion), buoyed by an 8.4% increase in private vehicle premium, which accounted for more than one-third of the total.

Homeowners’ premium grew 2.6% and commercial auto gained 9.8%, but specialty insurance fell 4.3% and commercial property declined 18%.

Catastrophe losses – including the impact from Texas hailstorms – increased to $US639 million ($853 million) from $US381 million ($509 million) in the corresponding period last year.

Net investment income grew to $US766 million ($1.02 billion) from $US687 million ($918 million).

Liberty is the fourth-largest property and casualty insurer in the US, and also operates in the Americas, Europe and Asia.

The company completed its acquisition of specialist international insurer Ironshore for about $US3 billion ($4.05 billion) earlier this month.