Updated

The nationalist Alternative for Germany party says it wasn't informed in advance that a group of benefactors planned to support its election campaign with free ads reportedly worth millions of euros.

Posters supporting the party, known as AfD, have appeared across North Rhine-Westphalia days before Sunday's election in Germany's most populous state.

German weekly Zeit reported Wednesday that the ads likely cost up to 4 million euros ($4.5 million.) Similar ads before other state elections prompted an investigation of possible illegal party financing, but officials found no wrongdoing on the part of AfD.

Regional party chief Marcus Pretzell said he didn't know who was behind the ads and expressed misgivings about them.

Pretzell told The Associated Press: "I would have, let's say, hoped that we hadn't acquired a sidekick we don't control."