Meanwhile, mediators tried to persuade the rest of the fractured rebel movement to join the process.
The peace agreement, reached with the Sudan Liberation Army of Minni Menawi on Friday after two years of sporadic negotiations, would help end a conflict that has killed at least 180,000 people in three years and left some two million displaced.
The suggestion that it allowed for a deployment of UN peacekeepers overturns previous rejections by Sudan's government, which so far has allowed only African Union (AU) peacekeepers on the ground.
In New York, John Bolton, the US ambassador, on Saturday welcomed Khartoum's "new willingness" to accept a UN peacekeeping force to take over from AU soldiers in Darfur region.
Citing the Sudanese government representatives' comments indicating they were now willing to accept the UN force, he said: "We view this as a very encouraging sign, the first positive outcome from the Abuja peace agreement.
The AU troops, now running out of funds, have largely been ineffective in stopping atrocities and re-establishing security, leaving tens of thousands to struggle in camps with little food or water.
The deal was struck only after intense pressure from the US. Robert B Zoellick, deputy secretary of state, went to Nigeria's capital to salvage the negotiations when they were deadlocked Monday, and George Bush, the US president, sent letters to rebel leaders and Sudanese government officials.
The peace deal calls for a cease-fire, disarmament of government-linked militias, the integration of thousands of rebel fighters into Sudan's armed forces and a protection force for civilians.
The deal calls for rebel fighters to
be absorbed into Sudan's army
But just a day later, mediators were still trying to persuade the splinter Sudan Liberation Army group of Abdulwahid El Nur to join the process, after he and several other members walked out of Friday's signing ceremony.
Fighting had intensified in recent days as well, which was interpreted as fighters jockeying for territory before the signing.
On Saturday, El Nur - who is backed by his Fur tribe, the largest in Darfur - met with Olusegun Obasanjo, the Nigerian president, after saying the peace deal was "criminal" and failed to adequately address core grievances that have festered over decades of neglect by the central government.
He demanded that the three Darfur states be incorporated into one autonomous region, that rebel movements have greater representation within the state legislature, that a second vice presidential position be created and held by a rebel officers, and that war victims be given hundreds of millions of dollars in compensation.
No new concessions
Mediators said they were offering no new concessions in the plan, which was backed by the AU, the US, Britain, the European Union and the Arab League.
Politically, the deal guarantees that rebel factions will have 21 of 73 seats in each of the three Darfur state legislatures, though the rebels wanted a majority of seats.
Zoellick admitted there was much work ahead. Getting a UN peacekeeping force on the ground was key, but would take at least six months, he said on Friday.
The peace pact won the backing
of the US, EU and Arab countries
Even then, Darfur "is going to remain a dangerous place. There is still a lot of distrust and fear", Zoellick said. There are "spoilers" who present "a reality and certainly a danger".
Mediators said, however, they were not reaching out to the smaller Justice and Equality Movement. The group, seen as militarily insignificant, has ties to Muslim conservative groups and wants regime change in Sudan. It vowed, nevertheless, to fight on.
"The war continues unless the root causes are addressed," said its chief negotiator, Hame Hussein.
The real rebel military power rests with Menawi's Sudan Liberation Army. Obasanjo praised Menawi during Friday's signing as "not just a good soldier, but a good statesman".
A cease-fire is supposed to take effect in a week, and within 37 days the government must move armed militia to restricted areas, remove heavy weapons and disarm the warring groups, Zoellick said.
While details for a UN peacekeeping force are finalised, the US diplomat said the US had asked Rwanda to send in some 1,200 troops to supplement the AU monitors.