STOCKHOLM (Reuters) -Swedish bank Handelsbanken reported its second-quarter profit well below forecasts on Friday, after a downturn in capital markets triggered a loss on hedging instruments.

Operating earnings at the 150-year-old rival to Swedbank fell to 5.25 billion Swedish crowns ($496.80 million) from 5.67 billion crowns a year ago. The mean forecast in Refinitiv poll of analysts had been for a profit of 6 billion crowns.

"The unusually severe downturn in the capital markets over a short period of time has led to a negative market valuation impact on our hedging instruments," Chief Executive Officer Carina Akerstrom said in the report.

But the effect would be reversed over time and lacked importance for the performance of the bank, she added.

Handelsbanken made a loss on financial transaction, which includes hedging instruments, of 147 million Swedish crowns, versus a profit of 429 million crowns a year ago.

Net interest income, which includes income from mortgages, came in at 8.39 billion crowns, higher than 7.57 billion crowns posted a year ago and 8.03 billion crowns in a Reuters poll of analysts.

Net commission income fell to 2.74 billion crowns from 2.77 billion a year ago and 2.86 billion in the poll.

($1 = 10.5676 Swedish crowns)

(Reporting by Johan Ahlander and Stine Jacobsen; Editing by Anna Ringstrom and Sherry Jacob-Phillips)