US bid to rescue Sudan elections after withdrawals
Key politician Sadiq al-Mahdi's is considering a total boycott
US envoy to Sudan Scott Gration is holding a second day of crisis talks after a boycott threatens Sudan's first multi-party national poll in 24 years.
Most major parties have withdrawn from the presidential elections and some groups have also pulled out of the parliamentary and municipal polls.
Several key parties in the north are also now considering a total boycott.
President Omar al-Bashir, wanted for alleged war crimes in Darfur, now faces only one major presidential challenger.
Veteran Islamist leader Hassan al-Turabi has confirmed that candidates from his Popular Congress Party would contest all the polls.
But the BBC's James Copnall in Khartoum says if the other parties go for a total boycott, the credibility of the elections would be damaged almost beyond repair.
The southern Sudan People's Liberation Movement (SPLM) - which serves in a coalition at national level with President Bashir - first announced it was boycotting the presidential election over fraud and security fears on Wednesday.
Zeinab Badawil, BBC News, Khartoum
The aim of the boycott is to rob President Omar al-Bashir of the opportunity to legitimise his rule.
He has governed Sudan for more than 20 years, but his indictment by the International Criminal Court on alleged war crimes in Darfur now hangs around his neck like a millstone.
He has been campaigning vigorously in the run-up to the vote on 11 April, travelling across Sudan, and was busy rallying his supporters in Sennar - east of Khartoum - as his opponents plotted their withdrawal.
His dilemma now is how to respond to the boycott. It is also a blow for Washington, which was laying a lot of store on these elections and wanted them to go ahead.
Other parties in the north followed suit, saying they believed the electoral process had been rigged in favour of Mr Bashir's National Congress Party.
They said the registration process had been flawed and their access to state media and rights to hold rallies restricted.
Then on Thursday evening a loose alliance of parties opposed to President Bashir announced their total withdrawal.
Spokesman Farouk Abu Issa said to go ahead with presidential, parliamentary and municipal vote would risk putting the country "on fire".
"So we ask[ed] for a postponement until we can get a conducive atmosphere for a fair election. The government said no and Bashir said no," he said.
Mr Gration is now trying to convince one of the main northern opposition politicians, former Prime Minister Sadiq al-Mahdi, his Umma party should contest at least some of the polls for parliament and regional governors' posts.
The party is currently debating whether to opt for a full boycott - if it does, all of the major opposition parties with the exception of Mr Turabi's are likely to follow suit.
Our reporter says it is believed Mr Mahdi will not return to the presidential race, but could let his party members contest the other elections.
Mr Gration said earlier that if the main opposition withdrew from the legislative elections it was not clear whether they would still be held.
Threat over referendum
SPLM presidential candidate Yassir Arman announced on Wednesday that he was pulling out of the election.
SPLM presidential candidate Yassir Arman: "There is continous control and rigging"
He also cited a lack of preparedness for the election in the Darfur region, where a rebellion has been taking place since 2003.
"The people of Darfur in the internally displaced people's camps asked the SPLM not to be involved in the election," he said.
The SPLM is still planning, however, to contest the parliamentary and municipal elections elsewhere in Sudan on the same day as the presidential poll.
Africa's biggest country
Deeply divided along religious and ethnic lines
11 April elections intended to be 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
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