US environmental regulators turned down Volkswagen's initial recall plan for its diesel cars equipped with illegal emissions cheat devices Tuesday, a day before its chief holds high-level talks on the scandal in Washington.

The California Air Resources Board rejected Volkswagen's recall proposals for its 2.0 liter diesels, and the federal Environmental Protection Agency agreed the plan was not acceptable.

CARB said VW's plans "are incomplete, substantially deficient, and fall far short of meeting the legal requirements" to rectify the emissions problem.

The EPA, itself awaiting VW's formal proposals, backed the California regulator.

"EPA agrees with CARB that Volkswagen has not submitted an approvable recall plan to bring the vehicles into compliance and reduce pollution. EPA has conveyed this to the company previously."

Volkswagen's chief executive, Matthias Mueller, is scheduled to meet in Washington with EPA head Gina McCarthy to discuss how the German automaker plans to deal with nearly 600,000 of its cars in the US equipped with illegal "defeat devices" that concealed excessive emissions.

The issue, which extends to 11 million VW, Audi and Porsche 2.0 and 3.0 liter diesel cars worldwide, has severely damaged Volkswagen's reputation and spawned a host of investigations in several countries.

In the United States alone the German company is facing potentially tens of billions of dollars in fines over the scandal.

CARB also issued an official notice of violation to Volkswagen on Tuesday formally outlining the ways its cars broke California regulations and listing some of the fines it could be facing.

"Volkswagen made a decision to cheat on emissions tests and then tried to cover it up," said CARB chair Mary Nichols in a statement.

"They continued and compounded the lie, and when they were caught they tried to deny it. The result is thousands of tons of nitrogen oxide that have harmed the health of Californians."

In response, Volkswagen said in a statement that it was working with outside advisers "to develop a swift, fair and independent program, which will provide a comprehensive remedy for our customers."

"We are committed to working cooperatively with CARB and other regulators, and we plan to continue our discussions tomorrow when we meet with the EPA."

The defeat device turns on pollution controls when the vehicle is undergoing emissions testing, and turns off when it is not being tested, allowing unauthorized amounts of poisonous nitrogen oxides to spew into the environment.

- 'We didn't lie' -

Volkswagen has been accused of foot-dragging in the US investigations into the scandal which emerged in the US in mid-September.

Mueller, in an interview Sunday with National Public Radio ahead of the Detroit auto show, called the illegal software "a technical problem" and said: "We had not the right interpretation of the American law."

Asked whether VW had an "ethical problem" for allegedly lying to the EPA to cover up the defeat device's existence, he denied it.

"We didn't lie. We didn't understand the question first," he said.

George Jepson, the attorney general of Connecticut, which is leading a separate probe involving more than 40 US states, slammed Mueller.

"Mr. Mueller's comments are disturbing, especially in light of the company's continued lack of cooperation with our investigation, and they underscore the importance of our inquiry as well as the investigations launched by other regulators," Jepson said in a statement Tuesday.

"We now learn that the company's newly appointed and most senior leader doesn't believe Volkswagen lied, which is undisputable, and cannot say when it plans to deliver its solution to a problem that is affecting millions of Americans, which is unacceptable."

On January 4, 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 also alleges VW had lied in its applications for the device to the EPA and CARB.