"Sudan has accepted the second phase of the agreement of UN support for the African force," Lam Akol, Sudan's foreign minister, told a news conference, adding that this included the sticking point of deploying helicopter gunships.
Khartoum's green light came after Ban Ki-Moon, UN secretary general, last week reassured Sudan that the helicopters would only be used for deterrence, not for offensive purposes.
The first two phases of the UN plan mainly involve logistical and technical support, but Sudan has yet to give the go ahead for the final phase which would see thousands of UN troops deployed.
Negroponte used a five-day trip to Sudan to press officials to accept UN peacekeepers to support what is the world's largest humanitarian effort.
"We must move quickly to a larger, hybrid United Nations-African Union peacekeeping force with a single, unified chain of command that conforms to UN standards and practices," he said.
The US official also urged rebel groups to join peace negotiations and Khartoum to comply with a peace accord signed last year by disarming the Janjawid militia which is accused of atrocities in Darfur.
"The government of Sudan must disarm the Janjawid, the Arab militias that we all know could not exist without the Sudanese government's active support," he said.
Khartoum has always denied backing the Janjawid, despite accusations by the UN and the AU.
Earlier, the Saudi Press Agency had reported that Sudan had signed an agreement, brokered in Saudi Arabia, on the deployment of African Union (AU) and UN forces in Darfur.