Volkswagen's top executives knew a year ago that some of the company's cars were markedly less fuel efficient than had been officially stated, Sunday paper Bild am Sonntag reported, without specifying its sources.

VW in early November revealed that it had understated the level of carbon dioxide emissions and fuel usage in around 800,000 cars sold mainly in Europe.

The scandal, which will likely cost VW billions, initially centered on software on up to 11 million diesel vehicles worldwide that VW admitted was designed to artificially suppress nitrogen oxide emissions in a test setting.

The Bild am Sonntag report contradicts VW's assertion, however, that it only uncovered the false CO2 emissions labeling as part of efforts to clear up the diesel emissions scandal, which became public in September.

A VW spokesman declined to comment on whether VW had knowledge already a year ago of overstated fuel efficiency.

Months after becoming aware of excessive fuel consumption, former Chief Executive Martin Winterkorn decided this spring to pull one model off the market where the discrepancy was particularly pronounced, the Polo TDI BlueMotion, the paper cited sources close to Winterkorn as saying.

The paper did not separately cite its sources for saying that top executives knew about the fuel usage problem a year ago, however.

VW at the time cited low sales figures as the reason for the withdrawal. The paper said that VW did not inform Polo TDI BlueMotion owners of the high fuel consumption, which was 18 percent above the nameplate value.

The VW spokesman reaffirmed the previously cited reason for the withdrawal.

"The offering of the Blue Motion TDI Polo was suspended in all markets due to subdued demand. We are currently testing all models built from 2012 for differences in CO2 levels from the listed values."

Winterkorn stepped down as CEO in September, following VW's admission that it had deceived U.S. regulators about diesel-car pollution.