Volkswagen chief executive Matthias Mueller on Sunday apologized for cheating diesel car emissions tests on his first official US visit since the scandal broke in September.

"We know that we have let down customers, authorities, regulators and the general public here in America," the head of the German carmaker said at a media reception on the eve of the Detroit auto show.

"We are - I am - truly sorry for that and I would like to apologize once again for what went wrong at Volkswagen," he added, stressing that "our most important task in 2016 is to win back trust."

"It's not only our cars we have to fix. We have to repair our credibility, too."

The Wolfsburg-based group admitted it installed software in around 11 million diesel cars of its VW, Audi, SEAT and Skoda brands worldwide that helped them evade emissions standards after US regulators discovered the problem.

The so-called defeat devices turn on pollution controls when the car is undergoing testing, and off when it is back on the road, allowing it to spew out harmful levels of nitrogen oxide.

The affair severely damaged Volkswagen's reputation and spawned a host of investigations in several countries.

The US government sued the carmaker for installing defeat devices on nearly 600,000 of its VW, Audi and Porsche vehicles sold in America between 2009 and 2015.

The complaint alleges that Volkswagen not only intentionally violated clean-air regulations but also obstructed the investigation by concealing facts and providing misleading information, despite the company's public pledges of cooperation.

Speaking to journalists after his speech, Mueller insisted that "we are not a criminal brand or group."

Volkswagen made "huge" technical mistakes, but had "no intention" to deceive the US public or regulators.

- Penalties could top $20 billion -

Civil penalties in the United States could run well above $20 billion. Volkswagen also faces a costly recall, and at least 650 class-action lawsuits from disgruntled US customers.

When asked about the fines, Mueller quipped that people "are overbidding each other every day" in their estimates.

"I am eager to see when the first one is writing about 100 billion," he told reporters, adding that "we have nothing to say about that."

Mueller confirmed that he will meet Environmental Protection Agency (EPA) administrator Gina McCarthy on Wednesday in Washington.

"We will offer some solutions and we will see how the reaction will be," he said.

"We have appropriate technical solutions. We will offer the solutions in very short time."

Mueller did not want to get into the details of the package, but when asked by AFP about a possible buyback of more than 100,000 affected vehicles in the United States, he said: "That is part of the solution we want to discuss with Mrs. McCarthy."

However, he said he expects "constructive talks" with McCarthy. He believes the package VW will present is "appropriate," but said "now we have to see if the EPA sees this in the same way."

The automaker is also working on an independent claims resolution program "which fits the problem and which is solving the problem." It will be handled by star lawyer Kenneth Feinberg, known for handling large consumer compensation cases such as the deadly ignition switches used in some General Motors cars.

German newspaper Bild am Sonntag reported on Sunday that VW engineers have come up with a technical solution for some 430,000 affected diesel cars. The vehicles would be refitted with a new catalytic converter to meet US emission standards.

The Volkswagen chief was tight-lipped about other scheduled meetings in Washington, and only said that he will meet "a lot of people."

Mueller also said Volkswagen plans to make an additional $900 million investment in the United States to build a new mid-size SUV.

The investment at VW's Chattanooga plant will create approximately 2,000 jobs, Mueller said.

"The US is and remains a core market for the Volkswagen Group," the CEO said.

Mueller remained bullish on the outlook for diesel, which is about 30 percent more efficient than gasoline engines and can help reduce greenhouse gas emissions.

"There will be a big future for diesel engines all over the world," he said.