FILE PHOTO: The Volkswagen logo is seen on the front of a car at the North American International Auto Show in Detroit, Michigan, U.S., January 14, 2019. REUTERS/Jonathan Ernst/File Photo

FRANKFURT (Reuters) - Volkswagen’s flagship VW brand missed its margin target in 2018 as operating profits declined despite growth in top-line revenues at the German carmaker, news weekly Spiegel reported on Friday, citing unpublished figures.

The operating margin at the brand fell to 3.8 percent from 4.1 percent, the magazine reported, putting it short of a target of 4 to 5 percent set by group CEO Herbert Diess, who wants to raise it to 6 percent over the medium term.

Volkswagen declined to comment on the report ahead of a news conference on its results scheduled for March 12. Another news conference on VW brand results is due a day later.

The company, based in Wolfsburg, reported preliminary 2018 group results a week ago that were weighed down by currency effects and supply bottlenecks caused by new emissions testing rules, and warned of a tough year ahead.