Darfur conflict causes its presidential hopeful to quit the race

South Sudan's leading party has withdrawn its candidate from the first multi-party elections the country has seen in 24 years.

Yassir Arman, leader of the Sudan People's Liberation Movement (SPLM), said he would boycott the April poll because of electoral irregularities and conflict in Darfur.il

The party is calling for the election, due to be held 11-13 April, to be postponed until November.

Arman was seen as the main challenger to President al-Bashir because he could attact voters from both the north and the south of the country.

"We decided that Yasir (Arman) should end his campaign for the presidency of the Republic," Riek Machar, the SPLM vice-chairman, told reporters.

Arman was the most credible opponent to incumbent Omar al-Bashir, who seized power in a bloodless coup in 1989 and has had a warrant for his arrest issued by the International Criminal Court (ICC).

The decision could affect the referendum to be held next year by the semi-autonomous south that will determine whether Sudan is split in two.

President al-Bashir had already threatened to cancel the referendum if the SPLM boycotted the election.

He said: "Holding elections in the Sudan is a national obligation that should be fulfilled."

The referendum was agreed under the peace agreement signed in 2005 to end the conflict in Darfur.

The civil war started between the Arab Muslim north and black Christian south started in 1983 and has claimed an estimated two million lives.