Liberty Mutual Insurance will combine its specialty lines business in the US with newly acquired specialist global insurer Ironshore, to create the nation’s sixth-largest underwriter of excess and surplus lines.

The Boston insurer’s specialty lines business, marketed as Liberty International Underwriters, will rebrand as Ironshore.

“The combination of our two operations will create a top-tier US specialty insurer with a broad and deep set of solutions for clients and brokers,” Liberty Mutual Chairman and CEO David Long said.

“For Liberty’s worldwide operations, Ironshore becomes an ideal complement to our $US5 billion ($6.75 billion) global specialty business by providing additional scale, expertise, innovation and market relationships.”

Ironshore Australia, part of Ironshore International, will continue to operate under its brand and in accordance with existing business strategy, MD Katherine Simmonds says.

“Currently there are no changes to announce for Ironshore Australia,” she told insuranceNEWS.com.au.

Liberty Mutual completed its $US3 billion ($4.05 billion) acquisition of Ironshore last week.