Austria's Constitutional Court has ruled that a presidential run-off election must be held again, handing a narrowly defeated candidate another chance to become the first far-right head of state in the European Union.

Norbert Hofer of the anti-immigration Freedom Party (FPO) lost the May 22 vote to former Greens leader Alexander Van der Bellen by less than one percentage point, with postal ballots having tipped the balance in Van der Bellen's favour.

The court on Friday said it was using a strict standard on the application of election rules.

Witnesses told it of irregularities in the way the count was carried out, including the processing of postal ballots sooner than they should have been.

Preliminary results during the count had put Hofer 3.8 percentage points ahead in the runoff for the largely ceremonial post of Austrian head of state, but postal ballots, which account for about 12 percent of eligible votes, swayed the result in Van der Bellen's favour.

A record 700,000 postal ballots were registered after the main count, dramatically putting Van der Bellen ahead by just over 31,000 votes in the final tally.

Austria election highlights anti-immigrant mood

Source: Agencies