"After the revelations putting the role of the European Commission into question, it is necessary that the European Parliament provide some transparency to the issue," said Greens MEP Karima Delli, after parliamentary group leaders approved the investigation.

The European Commission, the EU's regulatory arm, has drawn fierce criticism since the scandal erupted in September that it ignored evidence of Volkswagen using so-called defeat devices to pass pollution tests.

Defeat devices are sophisticated software fitted into diesel engines to skew the results of tests for nitrogen oxide emissions. It was the major discrepancies in test results, enabled by the devices, that prompted authorities in the US to confront Germany's Volkswagen, sparking the scandal that has rocked the auto industry.

The commission firmly denied the accusations that it failed in its regulatory duties and said it would cooperate fully with the inquiry.

"The Commission is more than ready to work with the European Parliament's Committee of Enquiry," a spokesman from the commission said. The commission also added that while it is responsible for setting pollution limits on cars and defining testing procedures, it has no control over enforcement, which is left to national authorities.

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