The EU urged Volkswagen Wednesday to hurry up its investigation into the pollution-cheating scandal after revelations that the row may also involve petrol engines and not just diesel.

The comments by the 28-nation bloc came as shares in embattled German auto giant took a renewed battering on the latest revelations.

"The commission invites VW to speed up its internal investigation," European Commission spokeswoman Lucia Caudet told a daily briefing.

"We need to clarify without delays what kind of CO2 irregularities were found, what has caused them, which cars are affected, where they were registered, what measures the group will undertake to remedy the situation."

Until now, the emissions-cheating scandal had centred on so-called defeat devices, sophisticated software fitted into diesel engines to skew the results of tests for nitrogen oxide emissions.

But late Tuesday, Volkswagen said that an internal probe had uncovered "inconsistencies" on carbon emissions, as well. And these might not only affect diesel engines, but the first petrol engines, too.

Caudet said Brussels had "not been notified, we do not have direct information" about the new findings.

The EU can impose penalties on automakers that fail to respect emissions targets but Caudet said that "first we need to establish the facts" before taking any action.

Volkswagen has found itself at the centre of a worldwide storm and the object of both regulatory and criminal investigations in a range of countries since mid-September when it admitted to fitting 11 million of its diesel vehicles with defeat devices. (AFP)