Sudan's former rebels launched their campaign on Sunday for the nation's first multiparty elections in 24 years.

The secretary general of the former rebel Sudan People's Liberation Movement (SPLM) said on Monday his country was on the brink of a new north-south civil war, and called on northern forces to leave a disputed oil town. "We're on the brink of war. Clashes have already happened," SPLM secretary general Pagan Amum told a news conference.

Thousands of civilians fled clashes between Sudan's former north-south civil war foes in the oil-rich central town of Abyei on Thursday. The clashes, sparked by a local dispute, highlight the tension in an area claimed by both Khartoum and South Sudan. More than three years after a 2005 peace deal, they have not agreed on borders or a local government for the region.

An unprecedented Darfur rebel attack on Khartoum is a turning point that could persuade Sudan's rulers to negotiate seriously with their foes or push Africa's biggest country towards disintegration. Sudan-watchers believe the key is international involvement and say much more pressure is needed on both rebels and the government.

Southern Sudan's Minister of Defence and a presidential adviser were among at least 23 people killed on Friday in a plane crash blamed on engine failure, officials said. "Two engines failed and there was nothing the pilot could do," First Vice-President Salva Kiir told a news conference.

Sudan's president promised on Wednesday there would be no return to civil war in Africa's biggest country in a speech that sought to calm tensions over a growing stand-off with the south. President Omar Hassan al-Bashir called on his political opponents to work with him "for the homeland".

Sudan's former foes have agreed on steps to implement a 2005 peace deal, First Vice-President Salva Kiir said on Sunday, indicating the country's worst political crisis in years may be resolved soon. The announcement raised hopes that ministers from the former southern rebel Sudan People's Liberation Movement's will soon return to the national coalition government.

Disarray in both government and rebel ranks makes quick progress unlikely in Darfur peace talks billed by the United Nations as a "moment of truth" to stop four-and-a-half years of violence in western Sudan. The best that can be hoped at the gathering in Libya, which begins on Saturday, is agreement to meet again.

Crisis talks between Sudanese President Omar al-Bashir and southern leader Salva Kiir ended on Thursday without agreement on getting his former rebels to rejoin the unity government they quit a week ago. The meeting at the presidential palace in Khartoum came the day after al-Bashir authorised a Cabinet reshuffle.

The two sides in Sudan's national coalition meet on Thursday to try to salvage their fragile peace deal after disenchanted former southern rebels walked out of the government. President Omar Hassan al-Bashir will meet First Vice-President Salva Kiir, chairperson of the Sudan People's Liberation Movement, in Khartoum.