US regulators said Monday Volkswagen's cars with larger diesel engines were also found to have violated the country's pollution rules.

The Environmental Protection Agency (EPA) said that in addition to cars with 2.0-Liter diesel motors that had used software thwarting laboratory emission tests, certain types of the company's 3.0-liter diesel vehicles also had so-called defeat devices to mask actual emissions of poison gases.

The violations cover models including the 2014 Touareg, 2015 Porsche Cayenne and the 2016 Audi A6 Quattro, A7 Quattro, A8 and Q5.

EPA officials indicated the German carmaker had installed its cheating software in big-engine vehicles from the model years 2014 to 2016. Reuters reported that Porsche cars also contained software to cheat emission tests, alongside certain VW and Audi models.

Scandal not dying down

The revelations were thought to be particularly bad news for the VW Group's newly appointed CEO, Matthias Müller, the former head of the Porsche brand.

The EPA told Volkswagen it was expanding its investigations. "VW has once again failed its obligation to comply with the law that protects air quality for all Americans," said Cynthia Giles, assistant EPA administrator.

A Volkswagen spokesman on Monday rejected the new accusations, saying no cheating software had been installed in 3.0-liter diesel engines to rig emission test results. He told AFP news agency his company would "fully cooperate with EPA regulators" to clear up the controversy.

The Wolfsburg-based company had admitted earlier it had installed defeat devices in 11 million cars worldwide with a view to falsifying emission tests. The company is already bracing for huge litigation and compensation costs.

hg/tko (AFP, Reuters)