* Parties could return if elections commission reformed
* Five candidates left against incumbent President Bashir
* U.S. envoy in crisis talks with political parties (Adds State Department comment, paragraph 11)
By Opheera McDoom
KHARTOUM, April 1 (Reuters) - Sudan’s main opposition parties have withdrawn from presidential elections, a senior member of one of the groups said on Thursday, a move that could wreck the looming vote and damage a faltering peace process.
“On the level of the candidates of the Presidency of the Republic, most of them (Sudan’s opposition groups) decided to withdraw,” said Mohamed Zaki, head of office for Sadeq al-Mahdi, leader of the opposition Umma party.
Zaki said only five independents and representatives of smaller parties were still in the race against incumbent President Omar Hassan al-Bashir in the oil-producing state.
Zaki said there was still a chance the main opposition candidates would review their decision if the government agreed to an overhaul of the country’s National Elections Commission, and responded to their complaints of widespread fraud.
Sudan’s presidential and legislative elections, due in less than two weeks, are central to the implementation of a 2005 peace accord that ended more than two decades of north-south civil war.
Thursday’s announcement came a day after south Sudan’s leading party, the former rebel Sudan People’s Liberation Movement (SPLM), withdrew its candidate, Yasir Arman, from the presidential poll, in protest against electoral irregularities and insecurity in Sudan’s western Darfur region.
The SPLM and opposition groups have demanded an investigation into how a government company won a tender to print voting papers and have made numerous complaints of fraud during voter registration and other preparations.
Washington’s Sudan envoy, Scott Gration, flew into Khartoum after hearing about Arman’s withdrawal and spent the day holding crisis talks with government and opposition figures.
“The Americans are here to save the process,” said the presidential candidate for the breakaway Umma Renewal and Reform party, Mubarak al-Fadil, after meeting Gration.
Fadil said Gration asked opposition groups to list their complaints about the poll preparations and offered to mediate with the government and election officials. Fadil was one of the candidates who later withdrew, said Zaki.
“We have concerns about the credibility of the election. We want to see it as inclusive and competitive as possible. Scott is there trying to help work here in the home stretch as we get ready for elections coming up,” State Department spokesman P.J. Crowley told reporters in Washington.
Sudan’s Communist Party told Reuters it had decided to boycott all levels of the April elections. The Popular Congress Party announced its presidential candidate, Abdullah Deng Nhial, would stay in the race.
No one was immediately available for comment from Sudan’s major opposition Democratic Unionist Party to confirm it had withdrawn its candidate alongside Umma.
The SPLM said it would also boycott all voting in Darfur, the scene of a seven-year conflict.
Analysts said Arman’s withdrawal effectively handed the presidential race to Bashir and could be part of a deal with Bashir’s northern-based National Congress Party to guarantee a referendum in January 2011, also promised under the peace deal, on independence for the south.
But Arman denied any deal, telling Reuters there was no point in participating in the election, and that the NCP had already rigged it for Bashir to win.
People in South Sudan said they were disappointed the SPLM would not field a contender against Bashir, but that the independence vote was more important to them.
“This election is not going to be free and fair — the NCP is going to rig it, everyone knows this,” said doctor Victor Jal. “What is important for us is just the referendum.” (Additional reporting by Andrew Heavens in Khartoum and Skye Wheeler in Juba and Andrew Quinn in Washington; writing by Andrew Heavens; editing by Mark Trevelyan)