Volkswagen AG took new steps on Monday to appease US customers and German union leaders unhappy with the company's response to a sweeping emissions cheating scandal that claimed another high-profile executive.

Volkswagen is offering a $1,000 credit, of which half is to be spent at VW and Audi dealerships, to US owners of certain diesel models that do not comply with government emissions standards, said VW's US subsidiary.

The automaker said eligible US owners of nearly 500,000 VW and Audi models equipped with 2.0-litre TDI diesel engines can apply to receive a $500 prepaid Visa card and a $500 dealership card, and three years of free roadside assistance services.

The move was VW's latest attempt to pacify owners who have been frustrated by how the German automaker plans to fix affected models. The company has warned it could rack up multi-billion-euro costs to remedy the issue and repair the damage to its reputation.

"I guess it's a very small step in the right direction. But far from what I'd like to see in terms of being compensated," said Jeff Slagle, a diesel Golf owner in Wilton, Connecticut.

The scandal erupted in September when VW admitted it had rigged US tests for nitrogen oxide emissions. The crisis deepened last week when it said it had understated the carbon dioxide emissions and fuel consumption of vehicles in Europe.

VW said on Monday it continues to discuss potential remedies with US and California emissions regulators, including the possibility that some of the affected cars could be bought back from customers.

In Washington, Democratic Senators Richard Blumenthal and Edward Markey on Monday decried VW's consumer programme as "insultingly inadequate" and "a fig leaf attempting to hide the true depths of Volkswagen's deception."

The senators said VW "should offer every owner a buy-back option" and "should state clearly and unequivocally that every owner has the right to sue".

Late on Monday, attorneys general from 47 US states and the District of Columbia issued a statement saying the automaker's offer to consumers "in no way diminishes the seriousness of the deceptive practices and environmental harms" being investigated by the states.

Slagle, who bought his vehicle in 2011, said he was surprised there was still no plans for how to fix the cars: "Even though they're clearly culpable, somehow they're in the driver's seat."

VW has said about 482,000 cars sold in the United States since 2009 with four-cylinder diesel engines had software installed that allowed the engines to pass government tests for smog-forming nitrogen oxide emissions, but pollute at levels far above government limits in normal operation.

The automaker posted details of its "goodwill package" at www.vwdieselinfo.com. Audi plans to post details of a similar programme on Friday.

VW said the customer offer did not cover models equipped with the 3.0 V6 TDI diesel engine, including the Touareg. The company last week told US and Canadian dealers to stop selling certain of those models from 2014-2016 after the US Environmental Protection Agency said VW group brands had installed illegal devices on some 3.0 V6 diesel models.

To qualify for the credit card offer, VW diesel owners must go to the company website, enter a vehicle identification number and provide mileage and contact information. VW will send the cards by mail. To activate the cards, owners then must take the vehicle to the dealer for verification.

VW said customers "don't have to sign anything" and will not be required to relinquish any legal rights.