Sudanese obstacles could mean the UN mission in Darfur is not viable, the head of UN peacekeeping has said.
Mr Guehenno said the UN has to ask whether a mission would work
Jean-Marie Guehenno told the United Nations Security Council that excessive demands from Khartoum "would make it impossible for the mission to operate".
Among other demands, Sudan wants advance notice of troop movements and to be able to shut down communications.
Mr Guehenno said the UN would have to consider whether a deployment would be worthwhile under such conditions.
The 26,000-strong United Nations and African Union peacekeeping force, Unamid, is due to take over protecting the people of Darfur in a month's time.
But Sudanese objections and delays, Mr Guehenno said, threaten the success of the mission.
As examples of the Khartoum government's reluctance to facilitate the practical preparations for Unamid, he said they were still awaiting:
- Authorisation for non-African troops
- Land for Unamid bases
- Authorisation for night flights.
Mr Guehenno said it would be impossible to operate in Darfur under such conditions.
The Unamid force is due to start its mission in a month
"Should the anticipated discussions fail to clear the path to the deployment of an effective force, the international community will be confronted with hard choices," Mr Guehenno said.
"Do we move ahead with the deployment of a force that will not make a difference, that will not have the capability to defend itself, and that carries the risk of humiliation of the Security Council and the United Nations, and tragic failure for the people of Darfur?"
Mr Guehenno added that Sudan's demands "create serious uncertainty with regard to the government's commitment to the deployment of Unamid."
The Sudanese ambassador responded by saying that the issues were only "administrative problems" which should not be exaggerated.
"The notion that Sudan is impeding is absolutely not correct," Abdalmahmood Abdalhaleem Mohamad told the BBC.
"The way they are reacting to these small administrative and legal issues under discussion really gives us the impression that they are not sincere," the ambassador said.
The Unamid mission is aiming to bring security to the Darfur region after more than four years of conflict.
But it has been plagued by problems, including a shortfall in resources and a lack of co-operation from both Western and African states.