Opposition candidates in Sunday's election in the Democratic Republic of Congo have refused to approve a statement aimed at reducing tension before the poll.
The elections are taking place two years later than scheduled and the run-up has been marred by violence.
Three leading presidential candidates held talks in the capital on Saturday.
But afterwards opposition figures Martin Fayulu and Felix Tshisekedi said they would not endorse the peace pact.
They said officials had rejected changes they had suggested to the text.
With less than a day before the election, there are concerns over groups not being allowed to vote, and over electronic machines being used for the first time.
What's the context for these elections?
If everything passes without incident, this will be the first peaceful transition in DR Congo since it gained independence from Belgium in 1960.
The current president, Joseph Kabila, took over from his assassinated father Laurent in 2001, but he is barred from running for another term under the constitution.
He was supposed to step down two years ago, but the election was postponed after the electoral commission said it needed more time to register voters.
The decision triggered violent clashes, as the opposition accused Joseph Kabila of trying to cling on to power.
Then last week, the election was delayed again, for seven days, because of problems deploying voting materials to polling sites.
This all came after thousands of electronic voting machines were destroyed in a fire in Kinshasa.
More on the DRC
What's the latest?
Three leading candidates and electoral officials met in a Kinshasa hotel on Saturday.
Leading opposition candidate Martin Fayulu, a former oil tycoon, had said the aim was to "sign an agreement which ensures we will all behave correctly during an after the electoral process".
But AFP later quoted Mr Fayulu as saying that he and Mr Tshisekedi, the son of a late long-term opposition leader, wanted amendments and refused to sign the text.
This week, voting in three districts was postponed until March, with the electoral commission blaming insecurity and an Ebola virus outbreak.
About 1.2m people will not be able to vote on Sunday as a result, in a country of close to 40m voters.
The decision in effect cancelled their votes, as the new president is due to be sworn in by mid-January regardless.
A crowd attacked an Ebola clinic in the east of the country after the announcement.
On Saturday, opposition candidate Theodore Ngoy tried to get the constitutional court to hold an emergency session to consider holding the vote in those areas.
But the BBC's Salim Kikeke in Kinshasa says the chances of the election being reinstated there are slim.
Separately, Mr Kabila gave a round of interviews on Saturday defending the record of a government that has been criticised for corruption and rights abuses.
He is backing former Interior Minister Emmanuel Ramazani Shadary in the election.
"I firmly believe that everything will be all right on Sunday," he told France's Le Monde newspaper.
Key presidential hopefuls:
What is the significance of DR Congo?
The vast central African state is rich in mineral resources and is the world's leading producer of cobalt, used to power mobile phones and electric cars.
However, it has high levels of poverty, bad infrastructure, and a political and business elite accused of enriching itself at the expense of the poor.
It has also been at the centre of what some observers call "Africa's world war", between 1997 and 2003.
The conflict, which dragged in regional states, claimed up to six million lives, either as a direct result of fighting or because of disease and malnutrition.