Germany's most senior figure in football is under investigation for alleged tax offences surrounding a secret payment to FIFA connected to the 2006 World Cup.

Officials from the prosecutor's office and tax police on Tuesday raided the headquarters of the German FA (DFB) in Frankfurt and the homes of association president Wolfgang Niersbach, a member of the FIFA and UEFA executive committees, and his predecessor Theo Zwanziger.

The investigation intensifies the pressure on Niersbach who had been seen as a likely future UEFA president. It centres on a the €6.7million payment made to FIFA in 2005 by the Germany 2006 World Cup organising committee.

An internal audit has failed to find any trace of the €6.7million in the DFB's tax documents but it has been claimed it was used as a slush fund to buy FIFA votes.

Documents and hard drives were seized from the DFB's headquarters and Frankfurt's senior public prosecutor Nadja Niesen said in a statement: "Fifty officials from the Frankfurt tax investigators as well as the prosecuting authorities carried out searches of the offices of the DFB as well as the homes of suspects.

"Prosecutors in Frankfurt have started an investigation on suspicion of serious tax evasion connected to the awarding of the 2006 World Cup and the transfer of 6.7million euros from the DFB to FIFA."

The payment was revealed by German news weekly Der Spiegel last month. Der Spiegel alleged the money had originally been loaned by former Adidas chief executive Robert Louis-Dreyfus, acting in a private capacity, to set up a slush fund to buy FIFA votes for the 2006 World Cup.

It claimed the money was later repaid to Dreyfus in 2005 using FIFA as cover - the German World Cup organising committee made a €6.7million contribution for a gala opening ceremony at Berlin's Olympic Stadium which was later cancelled.

Der Spiegel said the money was paid into a FIFA bank account in Geneva and from there transferred to a Zurich account belonging to Louis-Dreyfus, who has since died.

The Frankfurt prosecutor's statement added: "The defendants are accused of causing the submission of inaccurate tax returns as part of their former responsibilities."

Franz Beckenbauer, who lives in Austria, was president of the 2006 World Cup bid and last week admitted the DFB had made a "mistake" in paying the €6.7million, 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."

Niersbach has also denied any wrongdoing, and 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 6.7million euros 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."

Meanwhile, human rights groups have have lodged complaints with FIFA's ethics and electoral committees claiming presidential candidate Sheikh Salman, the head of the Asian football confederation, was involved in abuses of pro-democracy campaigners in Bahrain in 2011. He has denied any involvement.

The ethics and electoral committees will this week decide whether six of the seven FIFA presidential candidates will pass integrity checks. Suspended UEFA president Michel Platini's integrity check will not be made until his disciplinary hearing over a €1.8million payment to him from FIFA in 2011 is resolved.