DETROIT — Neither higher gas prices nor rising interest rates could put a damper on U.S. auto sales during the first half of the year.

Sales rose 1.8 percent during the period, with June sales increasing about 5 percent compared with a year ago, according to

Analysts said the boost was fueled by strong consumer confidence and low unemployment.

But analysts at Cox Automotive, which includes Kelley Blue Book, issued a cautionary note on the numbers, saying that much of the increase was due to low-profit sales to fleet buyers such as rental car companies, and retail sales to individual buyers were propped up by rising incentives such as rebates and subsidized leases.

Sales are “defying gravity,” said Jonathan Smoke, chief economist for Cox. “Retail sales have been flat, and even those sales have been supported by incentives being up 6 percent.”

Cox analysts also said rising interest rates and a possible trade war because of tariff threats by President Trump could raise new-vehicle prices and payments and cut into auto sales in the second half of the year. Still, given the fact that automakers are willing to spend to keep their share of the market, Cox analysts raised their full-year forecast by 100,000 vehicles to 16.8 million.

Trucks and SUVs accounted for 68 percent of the market in June, a record high as car sales continued to fade, Edmunds said.

Auto interest rates held steady in June, although analysts expect them to rise.

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