Insurance market Lloyd's of London reported pre-tax profit of £1.67bn for the first six months of this year, a 21% rise on last year's £1.38bn.
"While these results show an improvement over the equivalent period in 2013, the market conditions are becoming increasingly challenging," said John Nelson, chairman, and Inga Beale, CEO, in a joint statement.
"A weakening of the US dollar against sterling has had a slight negative impact on these results of 1% on net earned premium."
Investment income for Lloyd's rose to £642m, up from £247m on the previous year.
The market's combined ratio, which is the measure of how profitable it is in terms of how much premium is paid, rose to 88.2% from 86.9% - below 100% indicates an underwriting profit.
"In terms of claims, the first half of this year has been a relatively benign period for major catastrophes. The most notable claims have arisen from the unusually high incidence of aviation losses, which have been sudden and tragic," the chairman and CEO said.