Former US Secretary of State James Baker has resigned after seven years as United Nations mediator in the long-running conflict in Western Sahara.
James Baker: Referendum plan rejected by Rabat
The territory has been at the centre of a bitter dispute since former colonial power Spain pulled out in 1975, and neighbouring Morocco invaded it.
The Algerian-backed Polisario Front has been seeking independence since 1976.
Mr Baker is reported to have grown increasingly frustrated over his failure to broker an agreement.
His latest proposal was to make Western Sahara a semi-autonomous part of Morocco for four to five years, followed by a referendum allowing residents to choose between independence, continued semi-autonomy or integration with
This plan was rejected by Morocco, which refused to accept any loss of sovereignty over the area.
The vast north-west African territory is rich in phosphates and is also believed to have offshore oil reserves.
UN Secretary General Kofi Annan is expected to formally
announce Mr Baker's departure to the UN Security Council next
The official UN envoy for Western Sahara, Alvaro de Soto, will take over his work, a UN official told French news agency AFP. Mr Baker was a personal envoy of Mr Annan.
Ahmed Boukhari, a representative of the Polisario Front, described Mr Baker's resignation as a serious setback to UN attempts to resolve the Western Sahara issue.
"It's a great loss for the peace effort, but he has left
behind as his legacy a clear peace plan based on
self-determination for the people of Western Sahara," he
Morocco's ambassador to the UN, Mohamed Bennouna, told Reuters news agency: "We thank him for all his efforts and especially for his patience."
Algeria's ambassador to the UN, Abdallah Baali, said he was disappointed Mr Baker was stepping down.
"We have been impressed by his strong personality, his patience, his perseverance and his capability. He came up with very creative ideas and his last
plan received a favourable reception from the Security
The UN has spent more than $600m on peacekeeping efforts in Western Sahara as it has attempted to resolve the issue over the last 13 years.
Mr Baker was Secretary of State under the first President George Bush.
He served in President Reagan's administration as chief of staff and then Secretary of the Treasury.