German antitrust officials are investigating whether Amazon is preventing fair competition in the country's online marketplace.

The Bundeskartellamt (Federal Cartel Office) said in a press release Thursday it had "initiated an abuse proceeding" over the online giant's treatment of third-party sellers on the website Amazon.de.

"Because of the many complaints we have received we will examine whether Amazon is abusing its market position to the detriment of sellers active on its marketplace," said Bundeskartellamt President Andreas Mundt.

The statement added a list of practices that might be considered abusive practice by Amazon, including withholding payments, blocking seller accounts without explanation, and use of sellers' information.

The office said it would also closely examine if Amazon's dominance is hindering other online retailers and if sellers have become dependent on Amazon to make sales.

A separate investigation into Amazon's use of data is already underway by the European Union's Competition Commission.

Margrethe Vestager, who runs the commission, is targeting Amazon over concerns it is sucking up product data from successful rival sellers and then bringing cheaper copycat products to market.

The German cartel office said that while it would keep focusing on Amazon's impact on German sellers, the two probes would "supplement each other."

A spokesperson for Amazon told CNBC via email on Thursday that the firm was ready to "cooperate fully with the Bundeskartellamt and continue working hard to support small and medium-sized businesses."

The firm added that "tens of thousands" of small and medium sized German firms use Amazon.de, and through the platform more than 70 percent export products to customers around the world.

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