The emissions-testing scandal at Volkswagen AG widened Wednesday as the auto maker said the recall could include about 800,000 more cars than previously disclosed and that it would stop U.S. sales of certain vehicles.

Europe’s largest auto maker said it understated the level of carbon-dioxide emissions and fuel use of the additional cars to regulators. Some of the cars were gasoline-powered, Volkswagen said, moving the violations beyond the company’s diesel fleet for the first time.

German...