Turkish President Recep Tayyip Erdogan will lead Saturday prayers at Istanbul's iconic Hagia Sophia mosque, ahead of a battle for his political life against a powerful secular rival.

The 69-year-old will be emulating a ritual that Ottoman Sultans performed before they led their men off to war as he braces for Sunday's parliamentary and presidential ballot.

Erdogan has never faced a more energised or united opposition than the one led by retired civil servant Kemal Kilicdaroglu and his disparate alliance of six parties.

The Turkish leader excelled at splitting his rivals and forging unlikely unions while winning one national election after another over 21 years.

But his Islamic-rooted party is reeling from anger over Turkey's economic meltdown and a crackdown on civil liberties during Erdogan's second decade of rule.

The six opposition parties have put aside their political and cultural differences and joined forces for the lone task of pushing Erdogan out.

They are officially supported by Turkey's main pro-Kurdish party — a group that accounts for at least 10 percent of the vote.

'A very silly question'

The math is not adding up in Erdogan's favour and most polls show him trailing his secular rival by a few points.

Kilicdaroglu is now desperately trying to break the 50-percent threshold and avoid a May 28 runoff that could give Erdogan a chance to regroup and reframe the debate.

Turkish officials launched a formal investigation and made some arrests.

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