Opposition parties in Burkina Faso said preparations were on for "massive fraud" in Sunday's presidential election and threatened to not recognise the vote results.
Voting will take place in the shadow of a growing jihadist insurgency, with President Roch Marc Christian Kabore favourite to win re-election.
"It's clear that there is a huge operation orchestrated by those in power to carry out a massive fraud to legitimise," the re-election of the president, Zephirin Diabre, the main challenger to Kabore told reporters on Saturday.
"We will not accept results marred by irregularity," added Diabre, surrounded at a press conference by five of the other 11 opposition candidates, including Eddie Komboigo, the candidate of the party of former president Blaise Compaore.
Kabore can avoid a run-off election by winning more than 50 percent of the vote in Sunday's first round -- as he did in the last election in 2015. The president's camp is promising a repeat performance.
However his opponents say that will not be possible if the election is carried out fairly in the poor west African nation which has experienced multiple coups since gaining independence from France in 1960.
"It is absolutely inconceivable, having travelled the whole of Burkina Faso, to think of having a winner in the first round," said Diabre.
The security crisis has dominated the campaign and an undisclosed number of troops have been deployed for polling day in the landlocked West African country, one of the world's poorest.
The violence has forced one million people -- five percent of the 20 million population -- from their homes in the last two years, and at least 1,200 have been killed since 2015.
No votes in the presidential and parliament polls will be cast in one-fifth of the country's territory, where large swathes remain outside the state's control and jihadist attacks strike almost daily.
Most of the 12 opposition candidates running against Kabore have criticised the incumbent's failure to stem the bloodshed.
The fear of jihadist attacks on voting day is also on everyone's mind.