UN envoy Horst Koehler, a former president of Germany and ex-director of the International Monetary Fund, has invited the two sides along with Algeria and Mauritania to Geneva for talks on December 5-6.
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In letters sent to the four parties on Friday, the envoy requested a response by October 20, according to diplomatic sources.
Morocco and the Polisario Front fought for control of Western Sahara from 1975 to 1991.
Diplomatic efforts to end the conflict have been deadlocked since the last round of UN-sponsored talks in 2008.
Morocco maintains that negotiations on a settlement should focus on its proposal for autonomy for Western Sahara and rejects the Polisario's insistence on an independence referendum.
The Security Council in April approved a US-drafted resolution that urged Morocco and the Polisario to prepare for talks, setting a six-month deadline for action.
Algerian Foreign Minister Abdelkader Messahel told the UN General Assembly on Saturday that his government backed UN efforts to re-start talks on Western Sahara.
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He stressed that a solution must uphold the right of the people of Western Sahara to self-determination.
Morocco's Prime Minister Saadeddine Othmani told the assembly that Western Sahara was a source of instability in North Africa and accused Algeria of stoking the dispute.
The Security Council has extended the mandate of the MINURSO force in Western Sahara until October 31 and is expected to take stock of progress towards a political solution before that deadline.
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