The underwriter, which provides marine, casualty and property insurance and reinsurance, said pretax profit for the six months ended June rose 6 percent to $158.7 million, beating analysts' expectations of $153 million, according to company supplied consensus estimates.

Gross written premiums rose 2 percent to $1.15 billion in the period.

Premium rates for the business as a whole fell by 2 percent, with the steepest falls in Beazley's war, energy and terrorism businesses.

Beazley, which kicks off the Lloyd's of London half-year reporting season, said locally underwritten U.S. premiums grew 9 percent in the first half of the year.

"For as long as current market conditions prevail we expect growth opportunities for our London underwriters, who often specialise in catastrophe exposed risks, to be limited," the insurer said.

"By contrast, we continue to see attractive growth opportunities across our specialty lines portfolio."

The insurer's combined ratio was stable at 90 percent. A ratio below 100 percent means an insurer earns more in premiums than it pays out in claims.

Beazley said it would pay an interim dividend of 3.7 pence per share, up from 3.5 pence per share a year earlier and matching analysts' expectations.

Net investment income rose to $79.4 million in the period, compared to $62.7 million a year earlier.

Beazley has gotten approval from the Central Bank of Ireland for its Irish reinsurance business to become a European insurance company, giving it rights to operate throughout the European Union, even if Lloyd's loses access after Britain exits the bloc.

"Our U.S. operations performed strongly and our newly authorised Dublin based insurance company will support our growth plans in Europe, where we see opportunities to distribute our specialty products," Chief Executive Officer Andrew Horton said.

(Reporting by Noor Zainab Hussain in Bengaluru; Editing by Rachel Armstrong)