German police have raided the Frankfurt headquarters of Germany’s football association, the DFB, and searched the private homes of officials on suspicion of tax evasion linked to the awarding of the 2006 World Cup.

Documents and hard drives were seized from the DFB’s headquarters in Frankfurt, according to the German news agency DPA, which said 50 officers were involved.

“Prosecutors in Frankfurt have opened investigations on suspicion of serious tax evasion linked to the awarding of the football championship in 2006 and the transfer of €6.7m of the organising committee for the German Football Association (DFB) to the Fifa football association,” said prosecutors in a statement. They said they suspected the association of failing to register the payment in tax returns.

Bild had reported that the homes of the DFB president Wolfgang Niersbach and of the former president Theo Zwanziger had been raided. The DFB was not available for comment after several attempts by Reuters.

The parking place for the president of the DFB. Photograph: Ralph Orlowski/Reuters

Daimler, the main sponsor of the DFB, has called for a complete clarification of the tax-evasion allegations, saying: “We are monitoring the developments closely and expect a complete clarification.” Daimler’s Mercedes-Benz passenger car unit has been sponsoring the DFB since 1990.

The DFB released a statement saying it would co-operate with the investigation and that the organisation was not itself under suspicion.

The statement said: “The German football association (DFB) fully supports the investigation conducted by the Frankfurt prosecutor’s office on suspicion of serious tax evasion in connection with the awarding of the 2006 Fifa World Cup and the transfer of €6.7m from the World Cup organising committee to Fifa.

“On Tuesday morning officials from the prosecutor’s office and the tax police visited the association’s headquarters in Frankfurt am Main, and among other things secured documents.

“The DFB has told investigators it will co-operate fully. The prosecutors have informed the DFB that the investigation is limited to a suspicion of tax offences having taken place. The DFB itself is not accused of involvement.”

Niersbach has insisted previously that the committee behind the 2006 bid had acted both “fairly” and “legally”. “We secured the World Cup through fair means,” he said. “The World Cup was not bought. What was a summer fairytale remains a summer fairytale.”

Niersbach had been responding to allegations published in Der Spiegel that Germany’s World Cup bidding committee had established a slush fund to secure votes.

“The awarding of the 2006 World Cup was completely legal. There were no slush funds, and no vote buying,” Niersbach said.

Niersbach, 64, said the 10.3m Swiss francs paid to Fifa had been made to secure “organisational support in grants to the tune of 250m Swiss francs” and not to bribe Fifa functionaries.

Frank Beckenbauer, who was president of the 2006 World Cup bid and now lives in Austria, last week admitted the DFB had made a “mistake” in paying the €6.7m but denied that the money was used to buy votes.

He said: “In order to obtain financial support from Fifa, a suggestion by Fifa’s finance commission was followed which, in hindsight, should have been rejected. No votes were bought in order to win the right to stage the 2006 World Cup.”

The DFB had denied wrongdoing and said it had set up its own investigation into the payment. It said its inquiry had not found any evidence of wrongdoing, adding that it was also investigating whether it had any right to claim that money back, should it be proven that it was not used for its stated purpose.

“The DFB has not found even the slightest indications of irregularities during our investigation,” it said. “At the same time, there have been no indications at all of votes being bought from delegates as part of the bidding process.

“The payment [of €6.7m to Fifa in 2005] was in no way connected with obtaining the [World Cup] five years earlier.”