(Reuters) - Travelers Companies ( TRV ) reported a jump in second-quarter profit as higher investment income offset steep catastrophe losses, but lower-than-expected growth in net written premiums dragged the insurer's stock down 6.4% on Friday.

Even though customers are reviving spending on their insurance policies, weaker-than-expected growth in business insurance premiums hurt gains from personal and bond and specialty segments.

Net written premiums for the second quarter rose 8%, but fell short of analysts' expectations for 10% growth, according to LSEG.

Investor sentiment toward the industry was also soured by Selective Insurance, whose shares dropped 15% after it reported a surprise quarterly loss late on Thursday.

"Selective reported a very large reserve charge. Travelers has had kind of similar issues with reserves if you look under the hood of their results," said Piper Sandler analyst Paul Newsome.

"It's been masked by other positive things going on, but they've had similar concerns."

Travelers' underwriting gains jumped 55% while net investment income rose 24%, thanks to strong fixed income returns and growth in fixed maturity investments.

A steady U.S. economy, bets of interest-rate cuts and rising geopolitical uncertainty have helped fuel activity across U.S. equity markets, bolstering gains across investment portfolios.

However, severe wind and hail storms in the United States led to the insurer's catastrophe losses, net of reinsurance, rising to $1.51 billion from $1.48 billion a year earlier.

Its core income rose to $585 million, or $2.51 per share, for the three months ended June 30, compared with $15 million, or $0.06 per share, a year earlier.

The company's underlying combined ratio also improved to 87.7%, compared with 91.1% a year earlier. A ratio below 100% means the insurer earned more in premiums than it paid out in claims.

(Reporting by Noor Zainab Hussain in Bengaluru and Sinead Carew in New York; Editing by Devika Syamnath)