(CNN) -- A major opposition party has pulled out of parliamentary and local polls in Sudan's northern provinces, further destabilizing the electoral preparations.
A spokesman for the main political party the Sudan People's Liberation Movement (SPLM) confirmed to CNN that the party will boycott large parts of the vote in the north and Darfur. Several opposition parties have joined them.
The elections, set for April 11-13, were supposed to be the first meaningful democratic elections involving the whole of Sudan in over two decades, but they have been marred by widespread allegations of gerrymandering and vote rigging against the ruling National Congress Party (NCP).
Earlier this month the SPLM withdrew its presidential candidate, Yasar Arman, from the race against the incumbent President Omar Al Bashir.
On Thursday Under-Secretary-General for Peacekeeping Operations Alain Le Roy told reporters after briefing the Security Council: "We continue to express some concerns regarding aspects of the electoral environment. We have encouraged the government, the National Elections Commission and political parties to take steps to ensure respect for political freedoms and equal access to the media."
Though he said he had been encouraged by some steps taken by Sudan, he said it would be up to the 750 international and 18,000 domestic observers to assess whether the April 11-13 elections are legitimate.
The United Nations has been giving technical assistance and logistical support to the National Elections Commission.
Ambassador Susan E. Rice, U.S. permanent representative to the United Nations, was less diplomatic -- telling reporters she found much of what she had learned about Sudan's election preparations "quite disturbing."
Rice said Le Roy's briefing underscored U.S. concerns about government restrictions on political freedom, freedom of speech, freedom of association, the opportunity to campaign, harassment of the media and limitations on access to polling stations, particularly in the Darfur region.
The European Union's decision, announced Wednesday, to withdraw observers from Darfur "underscores just how insecure and problematic the electoral process is in that portion of the country, as well as elsewhere," she said.
Zach Vertin of the International Crisis group, said: "If these elections do not go according to plan and if a peaceful resolution isn't found then I think it is very possible that we will see a return to conflict in Sudan."
Fifty years of conflict between Northern and Southern Sudan killed more than two million people and the war formally ended in 2005 with the Comprehensive Peace Agreement (CPA).
The conflict pitted Northern Government troops against the Sudan Peoples Liberation Army (SPLA) and was a fight between Christian and Animist southerners against Muslim northerners.
The conflict in Darfur, which gained more international media coverage, was a different war and the violence there is regarded as genocide by the U.S. government and resulted in war crimes charges against Al Bashir.
Al Bashir seized power in a military coup in 1989 and brought in Sharia, the Islamic code for living. The implementation of Sharia created divisions between the north and south of the oil-rich nation. Southern Sudan is run as a separate territory from the north.
The elections were stipulated by the CPA as a stepping stone towards unity or separation of the north and south that is set to be decided in January 2011 by a referendum.
Some analysts have said that the elections are the "endgame" in the north whereas the referendum is more important in the south.
Analysts also say that as most of the oil is in the south, a split Sudan could negate sanctions to allow companies to prospect more easily in the South.
CNN's David McKenzie contributed to this report.