Volkswagen used devices to cheat air pollution tests in diesel luxury vehicles, U.S. environmental regulators said on Monday, in a new blow to the automaker already reeling from similar allegations regarding millions of smaller diesel engines. The U.S. Environmental Protection Agency said it is now looking at 3.0-liter V6 diesel engines used mostly in larger, more expensive models like the Porsche Cayenne sport utility vehicle in addition to engines on Jettas, Passats and other mass-market models whose test-deceiving software were initially targeted by the agency in mid-September.