The head of Russia's successful campaign to host the 2018 World Cup finals has again insisted there was no wrongdoing in its bid.

Swiss authorities have seized files and financial documents as part of an investigation into the bidding process for both the 2018 event and the 2022 finals in Qatar.

A FIFA report in the process, produced by lawyer Michael Garcia, was hampered after the computers used by the Russian team went missing -- meaning crucial evidence on its bid could not be examined.