Yassir Arman's decision could indicate splits among former rebels
A leading contender for president of Sudan has withdrawn his candidacy, casting more doubt over the country's first fully-contested poll since 1986.
The Sudan People's Liberation Movement (SPLM) said Yassir Arman would not stand against President Omar al-Bashir.
The SPLM - former rebels from the south - blamed the continuing conflict in the Darfur region and "electoral irregularities" for his withdrawal.
Sudan is due to vote in local, national and presidential polls on 11-13 April.
The elections have been delayed several times and observers and opposition parties have lobbied to have them delayed again amid fears of fraud and security concerns.
HIGH STAKES POLL
Africa's biggest country
Deeply divided along religious and ethnic lines
First multi-party national poll for 24 years
Continuing conflict in Darfur
President Bashir wanted for war crimes in Darfur
South Sudan rebuilding after 21 years of civil war
South Sudan may secede in 2011
Large oil fields near north-south border
But President Bashir, who seized power in a bloodless coup in 1989, is determined the vote will go ahead as planned.
While announcing Mr Arman's withdrawal, the SPLM made it clear that the party would field candidates in the other elections "across Sudan, except for Darfur".
The party said it could not put up candidates in Darfur because the region was still at war and under a state of emergency.
Northern opposition parties have already threatened to boycott the ballot box amid allegations of widespread fraud.
The BBC's James Copnall in Khartoum says they will decide on Thursday whether to take part.
Both the opposition parties and the SPLM - who serve in a coalition at national level with Mr Bashir - believe the electoral process has been rigged in favour of Mr Bashir's National Congress Party.
The opposition claims the registration process has been flawed and says its access to state media and rights to hold rallies were restricted.
US-based rights group Human Rights Watch has also criticised the government, saying the repression of the media and its opponents threatened a "free, fair, and credible" election.
The SPLM joined the unity government in 2005 as part of a peace deal ending a two-decade civil war.
Some 1.5 million people died in the conflict between the mainly Muslim north and the south, where most people are Christian or follow traditional beliefs.
The south, which is already semi-autonomous, is due to vote in a referendum next year which would see it gain independence from the north.