Austria's far-right party challenges election defeat

"The extent of irregularities is more than terrifying. That's why I feel obliged to challenge the result," he said.

FPO has filed a 150-page document which alleged that up to 570,000 votes were invalid.

Strache also claimed that postal ballots were illegally handled in 94 of 117 district election offices

FPO's presidential candidate, Norbert Hofer, who was not present at Wednesday's press conference in Vienna, lost to Alexander Van der Bellen, an academic, in the 22 May run-off by a tiny majority of just 31,000 votes.

"You don't have to be a conspiracy theorist to have a bad gut feeling about this whole election ... Without these irregularities Hofer could have become president," Strache told media on Wednesday.

Back in May, Hofer initially led the race, but lost to Van der Bellen after the postal votes were counted.

Austrian authorities have already said they are looking into alleged errors in the process.

Allegations concerning postal votes being opened too early would not be enough to change the final result of the ballot, however.

Van der Bellen, an independent candidate supported by the Green Party, is due to be sworn in to the largely ceremonial post on 8 July.

Austria's constitutional court has four weeks to rule on the appeal and to decide if there are grounds for a partial or full vote recount.

Its decision could result in fresh elections and its ruling could come just two days before Van der Bellen's swearing-in ceremony.

FPO, which had hoped to use the presidential vote as a springboard for parliamentary elections in 2018, leads opinion polls.

Its support is more than 30 percent bigger than either of the two centrist parties, the Social Democrats and the People's Party, which are currently in the ruling coalition.