Volkswagen Group's emissions scandal broadened Monday to encompass larger, more expensive vehicles with larger diesel engines, including Porsche and Audi sport-utility vehicles and luxury cars, as the Environmental Protection Agency cast doubt on the company's past statements about the situation.

The EPA accused VW of installing so-called defeat-device software on about 10,000 SUVs and additional luxury cars with a 3-liter diesel engine, not just the 482,000 smaller cars with the 2-liter engine previously implicated in the growing scandal.

The agency says it issued a second violation into addition to the one that rocked the automaker in September.

After the initial accusations, Volkswagen Group quickly admitted that it had flouted regulations by inserting software to defeat emissions testing on up to 11 million diesel cars worldwide, including certain versions of the Jetta, Passat, Golf and Beetle.

Monday's announcement broadens the scandal to SUVs, including the 3-liter diesel engine versions of the 2014 Volkswagen Touareg, the 2015 Porsche Cayenne and the 2016 Audi Q5.

The vehicles under suspicion now also includes some of Audi's plusher models, including the 2016 Audi A6 Quattro, A7 Quattro, A8 and A8L. Those vehicles are among Volkswagen Group's most profitable.

Unlike the initial violation, in which VW admitted culpability, this time it says it inserted no software to trick emissions testing equipment in the latest models. VW said in a statement that it "wishes to emphasize that no software has been installed in the 3-liter V-6 diesel power units to alter emissions characteristics in a forbidden manner." A VW spokesman, Mario Guerreiro, said he would not elaborate on the statement, including whether it means VW is denying that it cheated by any means.

In addition to marking the first time SUVs were included, Monday's announcement also dragged Porsche, another gem among VW Group's stable of brands, into the scandal. VW's new CEO, Matthias Mueller, took the top job in the wake of the scandal after heading Porsche.

The additional vehicles could expose the automaker to more than $375 million in Clean Air Act penalties — on top of the $18 billion in penalties the company could incur from the diesel car violations.

"We have clear evidence of these additional violations and we thought it was important to put Volkswagen on notice and to inform the public," Cynthia Giles, assistant administrator for EPA's Office of Enforcement and Compliance Assurance, told reporters on a conference call.

The EPA, California Air Resources Board and Environment Canada discovered the additional cheating while testing Volkswagen's vehicles. They have found nothing similar while conducting tests of other car companies.

Volkswagen engineers took a sneaky approach when fitting these vehicles with the "defeat device" software, the EPA alleged.

When the vehicles are undergoing federal emissions tests, software activates a "temperature conditioning mode" to fool regulators, Giles told reporters.

"At exactly one second after the completion" of those tests, Giles said, the vehicles flip back into "normal mode" and continue emitting nitrogen oxides are high levels.

Congress reacted with outrage at the latest allegations. "Today's revelation that Volkswagen's intentional deception of consumers is even more widespread than initially thought is deeply troubling and only further erodes American's faith in a company that many had trusted for decades," said Sen. Amy Klobuchar, D-Minn., in a statement. House Commerce Committee Chairman Fred Upton, R-Mich., and ranking member Frank Pallone, D-N.J., issued a joint statement in which they pointedly asked, "Where does VW's road of deceit end?"

It's yet to be see if the latest allegation damages VW's reputation further, but many owners have been braced for the worst, says Alexander Edwards, president of Strategic Vision, a consultancy to the automotive industry.

"The good news for Audi and VW is it's not going to do them any more damage -- just reinforce the damage that has already been done," says Edwards. "VW and Audi's number goal should be: How to do we develop a system to reinforce trust in our brand."