(Reuters) — Zurich Insurance Group Ltd.'s chief financial officer said low investment yields could persist "for some time," after flat returns and a strong dollar marred the underwriter's quarterly profit.

Europe's fifth-biggest insurer, like its rivals, has been struggling with rock-bottom interest rates and weak economic growth at home.

Zurich reported a 6% decline in first-quarter operating profit as the Swiss franc fell sharply against the dollar. Net investment return for the quarter was unchanged at 1%.

"Given that we're such a large fixed-income investor, interest rates will be the most significant determinant of when we'll see much higher yields, which means we'll be in a low-yield environment, potentially for some time," Chief Financial Officer George Quinn said.

Speaking on a call with reporters, Mr. Quinn also reiterated expectations that investment income would be $100 million lower this year at the underwriter's biggest unit, general insurance.

Gross written premiums at general insurance fell 5% to $10.1 billion, but rose 5% on a local currency basis.

Since the start of the year, the Swiss franc, in which Zurich writes its policies, has lost nearly 8% against the dollar, in which it reports.

Mr. Quinn said he did not expect currency movements to hurt Zurich's dividend, which is paid out in Swiss francs. The company pledged at the end of last year to raise its dividend.

He also said return on equity had fallen slightly below the company's target range in the three months to March 31.

Zurich's combined ratio deteriorated to 96.7% during the quarter from 95.9% a year earlier. A ratio below 100% means an insurer earns more in premiums than it pays out in claims.

The company's shares were down as much as 1.4% on Thursday morning on the SIX Swiss Exchange, placing it among the top five losers on the FTSE Eurofirst 300 Non-life insurance index.

Rivals such as Assicurazioni Generali S.p.A. have yet to report quarterly results, though Europe's biggest insurer, Allianz S.E., indicated on Wednesday that it would post a rise in operating profit.