Travelers Cos. Inc. reported lower second-quarter profit Thursday as higher-than-average catastrophe losses hit the insurer’s results.

Travelers reported 2017 second-quarter net income of $595 million, a 10% decrease from the same period last year. Net written premium grew 5% to $7.18 billion.

Travelers’ combined ratio deteriorated to 96.7% in the 2017 quarter, compared with 93.1% in the same quarter last year.

The insurer incurred $262 million in after-tax catastrophe losses in the quarter — $40 million more than the same period last year — in addition to significant noncatastrophe losses in its personal lines segments, Travelers CEO Alan Schnitzer said in a conference call with analysts.

Catastrophe losses for the first-half hit $488 million, he said. “This is our highest level of first-half catastrophe losses since 2011. While relatively high, the level of weather losses this quarter and year are within an over-time range that we plan and price for,” he said.

In the second quarter, Travelers reported $203 million in favorable prior-year reserve development, down from $288 million in the prior-year period. Commercial lines prior-year reserve development was $125 million, the same as last year’s second quarter, said Jay S. Benet, Travelers’ vice chairman and chief financial officer on the call.

There were no significant changes to Travelers’ catastrophe reinsurance treaties, which renewed on July 1, and the cost for the coverage was modestly lower, Mr. Benet said.

Travelers’ commercial insurance unit reported income of $429 million for the second quarter, up 7% over the same period last year, and net written premium of $3.54 billion, up 2%.

Travelers’ core middle-market business, which represents about half of its commercial insurance business, has seen steady increases in renewal premium, related to both rate and exposure increases, according to its investor presentation. Renewal premiums increased 3.5% in the second quarter, 2.6% in the first quarter and 2.3% in the fourth quarter of 2016.

For the first-half of 2017, net income fell 11% to $1.21 billion. Net written premium increased 5% to $13.14 billion.