President George W Bush has urged the Sudanese government and rebel leaders to bring the country's peace process to a successful conclusion.
Many parts of southern Sudan have been destroyed by the civil war
The US president spoke by telephone with President Omar al-Bashir, and with John Garang, who heads the Sudan People's Liberation Army.
He said the US-backed peace plan should be used as the basis for talks.
Negotiations to end Sudan's 20 years of civil conflict appear to have stalled on disagreements over power-sharing.
"The president indicated to both President Bashir and Mr Garang that there were moments in history when leaders must
rise to make a big difference for their countries," said White House press secretary Scott McClellan.
"This is that moment for Sudan."
Incentives to peace
The US wants the talks to be concluded by the end of March.
The Bush administration is concerned that Sudan has become refuge for al-Qaeda or similar organisations - Osama Bin Laden lived in Khartoum in the early 1990s when militant Islamists were dominant in northern Sudan.
Two key incentives for the government in Khartoum are the lifting of American sanctions and the dropping of Sudan from Washington's list of states it regards as sponsors of terrorism.
President Bush said Sudan's relationship the United States would only change when the deal was completed.
Apart from an 11-year period from 1972 to 1983, Sudan has been at war continuously since independence in 1956.
The civil conflict has pitted the Muslim north against Christians and animists in the south, and since 1983 has left some 2 million people dead.
A separate conflict developed a year ago after two armed groups in the western region of Darfur launched a rebellion.
The rebels say the government is neglecting and oppressing black Africans in favour of Arabs.
Hundreds of thousands have fled their homes and several thousand are estimated to have been killed.