Germany's Volkswagen (VW) said Tuesday an internal probe had found that 800,000 more vehicles showed "inconsistencies" on carbon emissions, including the first gasoline engines, as the auto giant sank deeper into a massive pollution cheating scandal. The company said initial estimates suggested the latest revelation could cost it 2 billion euros, but "a reliable assessment of the scale of these irregularities is not yet possible."

Separately, Porsche SE, the investment company that owns 32.4 percent of VW's capital, said Tuesday's revelations could have a "negative impact" on its own results, although it maintained its projections for 2015.

Porsche's North American subsidiary announced it was suspending sales of its Cayenne diesel vehicles until further notice, but stressed that customers could continue to operate their crossover cars.

Among the engines affected are 1.4, 1.6 and 2.0 liter motors of VW, Skoda, Audi and Seat vehicles, said a VW spokesman, adding that these cars had been found to be releasing more of the greenhouse gas CO2 than previous tests had shown. At least one gasoline engine is concerned, the company said. Up to now, only its diesel engines had been concerned. Volkswagen admitted in September that it had fitted 11 million of its diesel vehicles with devices designed to cheat official pollution tests, revelations that have sparked global outrage and investigations across the globe.

The so-called defeat devices turn on pollution controls when cars are undergoing tests and off when they are back on the road, allowing them to spew out harmful levels of nitrogen oxide. The latest issue opens up another front in the scandal engulfing the company as it relates to a different type of engine and emissions. It also comes a day after U.S. authorities accused the carmaker of also fitting the nitrogen oxide defeat devices on its larger 3.0 liter diesel vehicles - charges VW adamantly denied. "I have pledged from the start that we will stop at nothing in clarifying the circumstances," Volkswagen AG CEO Matthias Mueller said in a statement. "We will stop at nothing. It is a painful process but we have no choice," he added.

"The Volkswagen executive board regrets the facts established," he said of the internal probe that uncovered CO2 irregularities, adding that "the company will ensure that the correct emissions level are indicated following consultations with the authorities."

In the U.S., authorities late Monday accused VW of fitting illegal "defeat devices" not only on its smaller engines, but also into various six-cylinder 3.0 liter diesel VW Touareg, Porsche Cayenne and Audis.

The inclusion of Porsche vehicles among those alleged to contain defeat devices could trip up Mueller, who was drafted in from the luxury sports car unit to replace Martin Winterkorn, who resigned at the height of the scandal.

"We have clear evidence of these additional violations," said Cynthia Giles, an official with the U.S. Environmental Protection Agency's (EPA) Office of Enforcement and Compliance Assurance. "VW has once again failed its obligation to comply with the law that protects clean air for all Americans."

VW, the world's number-two carmaker by sales, had swiftly denied the new U.S. charges. "Volkswagen AG wishes to emphasize that no software has been installed in the 3-liter V6 diesel power units to alter emissions characteristics in a forbidden manner," it said in a statement. "Volkswagen will cooperate fully with the EPA [to] clarify this matter in its entirety."