Sudan has lifted its partial ban on United Nations operations in the conflict-hit Darfur region.
Two million people have been forced to flee the conflict
Khartoum had accused the UN of giving a helicopter lift to a rebel leader who opposes a recent peace deal.
The ban did not affect the work of the UN children's agency, Unicef, or of the World Food Programme, another UN body.
The UN is conducting the world's largest humanitarian operation in Darfur, where up to 300,000 people have died in three years of civil war.
A further two million people have been displaced as a result of the conflict and live in miserable conditions in refugee camps.
"The Sudanese government decided, effective today [Monday], to reverse its decision to suspend UN Mission in Sudan (UNMIS) activities in Darfur," spokesman Stephane Dujarric said.
Two smaller rebel groups did not sign the deal
The government in Khartoum had said that the UN had violated an agreement on its mandate by giving the rebel leader a helicopter ride on Saturday.
An official statement did not identify the leader, but the Reuters news agency reported it was Suleiman Adam Jamous, who has rejected a peace deal signed on 5 May.
Only one of the three Darfur rebel factions agreed to sign the peace deal.
The other two say the plan does not meet some of their basic demands, including proper compensation for war victims.
Mr Jamous was the humanitarian co-ordinator for the main rebel Sudan Liberation Army (SLA) before it split in November.
The leader of the SLA faction that signed the deal, Minni Minawi, imprisoned Mr Jamous for his opposition to the plan, rights groups and other rebel leaders have said.
UN officials and other groups were involved in securing his release.
The African Union-brokered peace plan has failed to end the violence in Darfur.
The UN has said it is considering sending troops to the region to supplement AU forces.
But Sudanese President Omar al-Bashir has opposed such a deployment, saying Sudan would not be "re-colonised".