By Neetha Mahadevan

FRANKFURT--German insurer Allianz SE said Wednesday it will restructure its U.S. property/casualty business Fireman's Fund, after struggling to bring losses under control.

Allianz said it will integrate Fireman's Fund's industrial and commercial insurance arm into the specialty insurer unit Allianz Global Corporate & Specialty, or AGCS. The combined business is expected to generate more than $3 billion in revenues, based on gross written premiums in 2013.

"With the repositioning of the commercial P&C insurance in the U.S., various options are being considered to also build scale for the personal lines business of Fireman's Fund," Allianz said about the retail arm of the fund, which accounts for about one third of the revenues of Fireman's Fund's business. For 2014, Fireman's Fund expects revenues of $2.8 billion.

Allianz bought the California-based Fireman's Fund in 1991, after which its marine business was integrated into AGCS in 2009. This integration brought nearly $600 million in annual gross premiums to AGCS.

The Fireman's Fund commercial P&C business focuses on declared areas of industry and product specialization, particularly those with domestic exposures across the U.S., while AGCS concentrates on large corporations or specialty risks, particularly those with multinational exposures.

Write to Neetha Mahadevan at neetha.mahadevan@wsj.com