AM Best has firmed the A- financial strength rating of Torus Specialty Insurance, the US underwriting unit of Bermuda start-up Torus Insurance Holdings.

Torus Specialty was previously known as Praetorian Specialty Insurance Company, which was acquired by Torus as a platform for expanding its US insurance business.

The rating agency's action removes the 'under review with negative implications' applied to Praetorian Specialty by AM Best on October 1 last year, when Torus acquired the company. Best also affirmed Torus Specialty's issuer credit rating at "a-". The outlook for the ratings is stable.

The lines of business written by Torus Specialty will be comparable to the lines written by other Torus operating entities, which include commercial property, onshore and offshore energy, construction, power utility and general casualty, Best said.

"AM Best anticipates that Torus Specialty will maintain strong risk-adjusted capitalisation, based on conservative performance expectations," the ratings agency added.

"The company is expected to produce good financial results supported by hardening rates in catastrophe-exposed classes. Additionally, Torus Specialty will benefit from the engineer site evaluations and technical pricing models that are embedded in the group's underwriting process."

Partially offsetting this was Torus Specialty's developing market profile. Torus Specialty will form the US trading operation of the Torus group, which started underwriting business in June 2008 and faces the considerable challenge of successfully growing its business profitably.