BERLIN, April 9 (Xinhua) -- The German Automotive Industry Association (VDA) has joined leading carmakers on Monday in rejecting calls for costly technical upgrades of diesel motors to lower nitrogen oxide emissions.

VDA president Bernhard Mattes told press at the "Future Mobility Summit" here that such hardware changes would be "very, very complex" and take two to three years.

"We do not have that much time," Mattes warned. He further emphasized that technical upgrades would make vehicles less efficient and hence lead to higher carbon dioxide emissions.

Earlier, the newly-installed German minister for the environment Svenja Schulze (SPD) urged carmakers to commit to technical upgrades for vehicles affected by the "dieselgate" scandal. According to the Federal Environmental Agency, technical upgrades of diesel vehicles are an expensive but effective means of preventing the imposition of outright driving bans enabled by a recent landmark court ruling in Germany.

Nevertheless, Mattes pointed to software upgrades as a more appropriate solution to help ensure that German cities complied with European Union clean air regulations.

The VDA president described media reports about a purported multi-billion-euro fund subsidized by the federal government to finance technical upgrades as "speculation" and defended modern diesel vehicles as no more polluting with regards to nitrogen oxide emissions than petroleum-powered cars.