Khartoum: Sudan's electoral commission on Friday dismissed calls by opposition candidates for a postponement of general elections and said the vote will take place as scheduled from April 11 to 13.

"The electoral commission ensures that the elections will take place as envisioned, on April 11 to 13," commission official Abdullah Ahmad Abdullah told reporters after a meeting with US Sudan envoy Scott Gration.

One of Sudan's largest opposition parties said on Friday it would boycott presidential, legislative and gubernatorial polls if government did not meet demands, including a four-week postponement within four days.

The opposition Umma Party had said on Thursday it was united with Sudan's other main political parties to withdraw their presidential candidates from the race. This was intended to discredit incumbent Omar Hassan Al Bashir's bid to secure a new term in oil-producing Sudan.

The new decision followed a six-hour meeting of the party's political bureau. Sources said the rank and file, who had spent money and time campaigning wanted to continue with the polls, despite accusations of widespread fraud.

"If these eight conditions are not fulfilled by April 6, the Umma party will boycott all the process of elections," Sara Luqd Allah, a senior party official told reporters.

Al Bashir's ruling National Congress Party has repeatedly said it will not accept any delay to the polls due to start on April 11 in Africa's largest country, the first multi-party vote in 24 years.

Luqd Allah said US envoy Gration had told Umma party leader Sadeq Al Mahdi in a morning meeting that he "would try to achieve the delay."

In Washington the State Department said legitimate concerns had arisen in the run-up to the election and that Gration would continue to press for maximum participation in the polls, which should come on schedule.