A leading contender for president of Sudan has withdrawn¹ his candidacy, casting more doubt over the country's first fully-contested poll since 1986.

苏丹一位主要总统候选人放弃候选资格，使该国自1986年以来的首次全民选举产生了更多的疑问。

Yassir Arman's decision could indicate splits among former rebels

The SPLM - former rebels from the south - blamed the continuing conflict in the Darfur region and "electoral irregularities" for his withdrawal².

Sudan is due to vote in local, national and presidential polls next month.

The elections, scheduled for 11-13 April, have been delayed several times and observers and opposition³ parties have lobbied（游说） to have them delayed again amid fears of fraud and security concerns.

But President Bashir, who seized power in a bloodless coup⁴ in 1989, is determined⁵ 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.

Not free, not fair

Meanwhile, northern opposition parties have already threatened to boycott⁶（联合抵制，拒绝参加） the ballot⁷ box amid allegations（辩解，断言） of widespread fraud.

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 coalition⁸（联合，结合） with Mr Bashir - believe the electoral process has been rigged（操纵，控制） in favour of Mr Bashir's National Congress Party.

The opposition claims the registration⁹ 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 repression¹⁰ of the media and its opponents threatened a "free, fair, and credible¹¹" election.

The SPLM joined the unity¹² 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 Christian¹³ or follow traditional beliefs.

The south, which is already semi-autonomous（自治的，自主的） , is due to vote a referendum（公民投票） next year which would see it gain independence from the north.